The Global Mental Health Assessment Tool--Primary Care Version (GMHAT/PC) is a computerised clinical assessment tool developed to assess and identify a wide range of mental health problems in primary care. It generates a computer diagnosis, a symptom rating, a self-harm risk assessment, and a referral letter. Patients from primary care and community psychiatric outpatient clinics and a small sample of inpatients were interviewed for a period of two months using the GMHAT/PC. A proportion of patients were simultaneously rated by a psychiatrist and a general practitioner for inter-rater reliability. All patients also completed the Hospital Anxiety and Depression Scale (HAD). To conduct the interview was easy in all settings and took 10-15 minutes for patients who had psychiatric symptoms. Inter-rater agreement on mental state symptom groups ranged from 0.49 to 1 (kappa). The computer diagnosis correlated highly with the clinical diagnosis and there was a good level of agreement between HAD ratings and GMHAT/PC ratings. These data suggest that the GMHAT/PC is an easy to administer computerised tool which can be used in primary care for the standardised assessment of mental health problems.