Background: A population sample of people with Down syndrome, studied from infancy, has now been followed up at the age of 50 years. From the original sample of 54, there were 27 still in the study at the age of 50, all but four of the losses resulting from deaths. Methods: Intelligence and language skills were tested and daily living skills assessed. Memory/cognitive deterioration was examined using two test instruments. Other aspects of the people's lives were examined via carers' reports. Results: Scores on verbal tests showed little change. Those on a non-verbal test, on self-help skills and on both memory tests showed some decline, even when the scores of those already suffering from dementia were discounted. Conclusions: At the age of 50, those not already diagnosed with dementia showed some decline on most tests. While this may include scores of people who subsequently develop dementia, it may also reflect the normal ageing process in this population.