AESOP-10 is a longitudinal study of 557 individuals with a first episode of psychosis recruited from South East London and Nottingham in the United Kingdom. Participants were originally identified between September 1997 and August 2000 through systematic screening of all inpatient and outpatient mental health services within defined catchment areas, and the baseline sample also included healthy community controls, although these were not re-contacted at follow-up. The cohort comprised adults aged 16 to 65 years at first presentation, from diverse ethnic backgrounds. Recruitment focused on all incident cases of psychosis. At follow-up, participants were traced and re-contacted approximately 10 years after baseline to collect detailed information on clinical, social, and service-use outcomes. There are plans for further long-term follow-up to examine trajectories over 25 years.