Failing to realise intentions in the future is a common weakness in persons with intellectual disability. Despite research in different clinical groups, prospective memory has received little attention in relation to intellectual disability. A common view is to identify a prospective part (when to act/timing) and a retrospective part of prospective memory (what to do/plan). Retrospective memory and vigilance are important for execution in prospective memory in persons with intellectual disability. A group with intellectual disability (IQ < 70, n=58) was defined together with a control group matched on age, sex, level of education and years of education (n=116) in the Swedish Betula database. The controls perform better than persons with intellectual disability on the prospective memory task. About half of the participants with intellectual disability remembered the retrospective part of the prospective memory task if the experimenter provided a cue. Persons with intellectual disability were able to perform on the prospective memory task, despite performance at floor level for verbal prospective memory tasks in previous studies. A possible explanation is that no monitoring was required as the ongoing task was performed. The context formed by having finished all other memory tasks may have been easier to remember.