Children with learning disabilities face inconsistencies and weaknesses when transferring into adult services in Northern Ireland, their Commissioner said.
Gaps and flaws in the transition arrangements for education, health and social care systems mean they do not always receive adequate support on leaving school, added Patricia Lewsley-Mooney.
They also do not always have accurate information on the range of accommodation and health services on offer or their eligibility for them, said a report for the Children's Commissioner.
Ms Lewsley-Mooney said: "The transition to adulthood should be a time of excitement and opportunity. However, for young people with learning disabilities and their families, it is often a time of stress and anxiety about the possible loss of support and services which are currently in place, and uncertainty about the future."
The Review of Transitions to Adult Services for Young People with Learning Difficulties found inconsistencies, weaknesses and gaps in arrangements for children with learning disabilities moving from child to adult services.
Barbara Green, principal of Beechlawn School in Hillsborough, said: "Whilst many of our pupils benefit from services provided by regional colleges and organisations such as Stepping Stones and Mencap, other more vulnerable pupils, especially those on the autistic spectrum, need more choices.
"They are unable to stay at this school past the age of 16 and therefore decisions are made about their lives that are based on what is available to them rather that what is in that young person's best interests."
The report by Queen's University Belfast researchers considered transition arrangements for young people with learning disabilities across education, health and social care and employment.
According to the report, young people with learning disabilities are much more likely to experience mental health problems.
The research said there needs to be support and information for young people shifting to adult mental health services, in and out of acute hospital care, and involving sexuality and relationships education.