OBJECTIVE Adaptive behaviour in Down syndrome is described to increase until middle childhood and to begin to decline in adolescence, whereas significant deterioration in middle adulthood has been attributed to early onset of dementia. Nevertheless, opinions diverge about when the slowing down of adaptive and cognitive abilities starts. Our aims were to describe the profile of adaptive behaviour in Down syndrome, the variability within different age-groups, age-related changes and the correlation to cognitive abilities. METHODS In a prospective cross-sectional study, individuals with Down syndrome all living in the family and without signs of dementia in 4 Italian sites were included and performed a detailed medical and neuropsychiatric work-up, as well as cognitive testing and adaptive behaviour, using the Vineland Adaptive Behaviour Scales. RESULTS Seventy-five individuals with Down syndrome from 4 to 52 years were included. Adults from 20 to 30 years showed the highest performance of all groups. The area of communication, always an area of strength, did not change over time, in childhood and especially in adolescence daily living skills (p = 0.012) and socialisation (p = 0.021) scored on average, whereas in young and middle adulthood performance in daily living skills and socialisation and were areas of strength. CONCLUSIONS Individuals with DS continue to increase competence in adaptive behaviour until 30 years, even when cognitive abilities reach a plateau. We found no major decline in middle adulthood. This may be due to exposure to daily life, but needs to be supported by further studies.