BackgroundDecline in social functioning occurs in individuals who later develop psychosis.AimsTo investigate whether baseline differences in disability are present in those who do and those who do not make a transition to psychosis in a group clinically at high risk and whether disability is a risk factor for transition.MethodProspective multicentre, naturalistic field study with an 18-month follow-up period on 245 help-seeking individuals clinically at high risk. Disability was assessed with the Disability Assessment Schedule of the World Health Organization (WHODAS–II).ResultsAt baseline, the transition group displayed significantly greater difficulties in making new friends (z =−3.40, P = 0.001), maintaining a friendship (z =−3.00, P = 0.003), dealing with people they do not know (z =−2.28, P = 0.023) and joining community activities (z =−2.0, P = 0.05) compared with the non-transition group. In Cox regression, difficulties in getting along with people significantly contributed to the prediction of transition to psychosis in our sample (β = 0.569, s.e. = 0.184, Wald = 9.548, P = 0.002, hazard ratio (HR) = 1.767, 95% CI 1.238–2.550).ConclusionsCertain domains of social disability might contribute to the prediction of psychosis in a sample clinically at high risk.