BACKGROUND: Psychiatric clinics have high non-attendance rates and failure to attend may be a sign of deteriorating mental health. AIMS: To investigate why psychiatric out-patients fail to attend, and the outcome of attenders and non-attenders. METHOD: Prospective cohort study of randomly selected attenders and non-attenders at general adult psychiatric out-patient clinics. Subjects were interviewed at recruitment and severity of mental disorder and degree of social adjustment were measured. Six and 12 months later their engagement with the clinic and any psychiatric admissions were ascertained. RESULTS: Of the 365 patients included in the study, 30 were untraceable and 224 consented to participate. Follow-up patients were more psychiatrically unwell than new patients. For follow-up patients, non-attenders had lower social functioning and more severe mental disorder than those who attended. At 12-month follow-up patients who missed their appointment were more likely to have been admitted than those who attended. CONCLUSIONS: Those who miss psychiatric follow-up out-patient appointments are more unwell and more poorly socially functioning than those who attend. They have a greater chance of drop-out from clinic contact and subsequent admission.