HEN Susan Colacello says she is afraid of death, she doesn't mean it in the generic way that most people use the phrase. Her fear is very specific. She doesn't want to die because she worries what will become of her son, Kevin, who has Down syndrome.

"I'm in a group of mothers who have disabled kids, and we all share the same thing," said Mrs. Colacello, 42, who lives in West Windsor, N.J. "We're terrified of dying."

For the parents of disabled children, that is often the essence of retirement and estate planning. There are few idyllic thoughts of golf courses and warm weather, few pleasant musings about who should inherit the family antiques. Instead there is dread, an underlying knowledge that no matter how many arrangements have been made and how much money has been provided, no one will care for a child with Down syndrome or autism or cerebral palsy the way parents have.

That worrying starts early: Kevin is only 3. And it is difficult to escape. Betty Stone of Des Plaines, Ill., also has a son with Down syndrome, but he is 40, and she is 81.

"My main concern is the future," said Mrs. Stone, whose husband died six months ago. "That's the big concern for all parents, no matter how old your child is."

There was a time when few parents worried that their disabled children would outlive them. Early intervention and improved health care have changed that. The mean age at death for a person with mental retardation was 18.5 in the 1930's, but by 1993 it was 66.2, one study found.

As longevity was increasing, the notion of placing severely disabled people in large, impersonal institutions was being discredited. In a 1999 study, David Braddock, now at the Coleman Institute for Cognitive Disabilities at the University of Colorado, calculated that almost 480,000 developmentally disabled people were living with family caregivers age 60 or older, with another 1.4 million living with family members younger than 60.

All this has turned estate planning into a financial and emotional maze for parents with disabled children. The government, in its Kafkaesque way, is both godsend and hindrance, providing a safety net but setting out an exacting procedure for any parent who wants to do more than that.

Federal and state programs pay for the basic care of a disabled adult; parents need not fear that their child will end up in the street. But the government generally does not pay for enhancements that parents view as crucial for their children — special camps, visits with relatives, private health insurance, therapeutic recreation like horseback riding and hundreds of other things. And, of course, many parents do not want to leave their disabled child at the mercy of the government, with its ever- changing cast of administrators and fickle budgets.

Yet if the disabled person has more than $2,000 in assets, the government claims them to cover its own costs, so leaving money to a disabled child in a traditional will does nothing. The government, though, has created a way around the $2,000 hurdle: parents can establish what is called a special-needs trust, using life insurance, real estate and other assets to create a fund that can pay for an enhanced life while leaving basic benefits like Supplemental Security Income intact.

Such is the planning gantlet parents of disabled children must run. That's the easy part. Going through the financial planning process, parents say, forces them to confront difficult, draining questions, like: What, exactly, are our child's long- term prospects? Who might be willing to act as guardian? Should we expect our nondisabled children to care for their sibling? What about our own hopes for retirement?

Like many parents, Susan and Albert Colacello put off facing those issues. Kevin makes procrastination easy; he is high-functioning for a child with Down syndrome, active and mischievous.

"You sometimes forget," Mr. Colacello, 40, said the other day, watching the boy wreak havoc in the living room like any other toddler. "And then the reality sets in: someone's going to have to take care of him."

An insistent aunt finally nudged the Colacellos toward a lawyer's office. So did the attacks of Sept. 11.

"We lost a really good friend," Mrs. Colacello said, "and he had his affairs really in order. It made things so much easier for his family." Last month the Colacellos signed documents creating a special- needs trust and establishing guardianship. They achieved a measure of security but lost some dreams. "This is a very necessary thing, but the reality of doing it really shatters your hopes," Mrs. Colacello said. "It's just a constant reminder that Kevin is never going to be able to make decisions."

And, she said, it is often jarringly at odds with the upbeat message that veterans in the world of disabilities use to ease the way for newcomers.

"On the one hand," Mrs. Colacello said, "we're supposed to feel that Kevin didn't change our lives. We're supposed to be positive. But Kevin can't even own anything."

The Colacellos know that the plans they have created will need to be revisited as Kevin ages. One delicate point will be what role his older brother, Christopher, now just 7, will play.

Rosalind and Joe Vargo of Syracuse, at 48, are just a few years older than the Colacellos, but they already have two decades' worth of experience dealing with such issues. Their daughter, also named Rosalind — Ro — is 21 and has Rett syndrome, a little-known neurological disorder that leaves its victims unable to talk and impairs cognition, mobility and muscle control.

Mrs. Vargo has a vivid memory from 20 years ago, when her daughter's disabilities were becoming evident, and a neighbor asked, "When are you going to send her away?" Though that is exactly what many parents were doing then, it was an image Mrs. Vargo could not bear.

"I was having nightmares that Ro would someday die alone in one of those developmental centers," she said. "That's not what we had dreamed, and that's not what we envision, now or when we're gone."