OBJECTIVE--To assess the health status of patients with 11 common illnesses--asthma, diabetes, arthritis, back pain, sciatica, hypertension, angina, anxiety, depression, and heart attack and stroke. DESIGN--Face to face interview using a structured questionnaire which contained the Short Form 36 questionnaire (SF-36) and questions on lifestyle, health service utilisation, and self reported conditions treated by physicians. SETTING--Patients' homes, in West Glamorgan, Wales. SUBJECTS--Twelve hundred adults, aged 20-89 years, were randomly selected from the register of the family health services authority. MAIN OUTCOME MEASURES--The eight scales within the SF-36 health profile. RESULTS--The response rate was 82%. Each illness had a distinctive profile; patients with anxiety or depression reported the worst health experience in role limitations because of emotional problems and mental health, while patients with back pain, arthritis, or sciatica registered the three highest negative scores in bodily pain and role limitations due to physical problems. For all disease groups, the general health perceptions of those with the disease was significantly worse than those without it (p < 0.01). CONCLUSIONS--The SF-36 allows comparison of the health status of patients suffering from different conditions. Data such as these can be used to inform better purchasing decisions on how resources might be more effectively deployed and as a bench mark to monitor the effects of multiple health care interventions by conducting serial surveys.