Psychosocial rehabilitation in forensic psychiatric services requires sound measurement of patient and staff perceptions of psychosocial function. The recommended World Health Organisation Disability Assessment Schedule 2.0 (WHODAS), designed for this, has not been examined with offender patients. To examine patient and staff WHODAS ratings of secure hospital inpatients with psychosis, any differences between them and explore associations with other clinical factors. Seventy-three patients self-rated on the WHODAS after 3months as inpatients. An occupational therapist interviewed the patient's primary nurse and care team at about the same time (staff ratings). Scores were calculated according to the WHODAS manual. WHODAS scores and interview-rated symptom severity, cognitive measures, daily antipsychotic dose and duration of care were compared. Patient ratings indicated less disability than staff ratings for total score and for the domains of understanding and communicating, getting along and life activities. Self-care and participation ratings were similar. Patients were more likely to rate themselves as disabled in getting around (mobility). Only one-fifth of patient- and staff- ratings (16, 22%) were similar, while for nearly a third of the patients (23, 32%) self-ratings were higher than staff ratings. More severe positive symptoms were associated with higher self-rated WHODAS disability after accounting for treatment duration, negative symptoms, cognitive score and antipsychotic dose. No variable accounted for the staff/patient differences in ratings. Our mean WHODAS score findings echoed those in other patient samples-of patient underestimation of disability, linked to severity of symptoms. In this study using the WHODAS for the first time in a forensic mental health secure inpatient service, however, we found that, by comparing individuals, half of the patients reported equivalent or greater disability than did staff. Future research should focus on elucidating from patients what contributes to their self-ratings. Understanding their thought processes in rating may enhance rehabilitation planning.