In a comparative study 1720 healthy persons from the general population and 242 hospital patients with the ICD-10 diagnosis Cancer, Heart Disease, Diabetes, Multiple Sclerosis, Arthritis, Diseases of the Respiration System and Schizophrenia completed the WHOQOL-BREF. The results of comparative multiple regression analysis show that the different diseases have a characteristic impact on the four subscales of the WHOQOL-BREF. Somatic diseases were found to have a strong negative impact on physical health, psychological well-being, and overall quality of life but not on social relationships. Among the somatic diseases only arthritis and multiple sclerosis had a significant negative impact on the environmental domain of quality of life. Schizophrenia was found to have a significant negative impact on physical health, psychological well-being, social relationships, environment, and on overall quality of life. For the different somatic diseases the results of the study indicate that a decrease in quality of life is not primarily a result of the severity of the disease in the sense of its mortality, but more a result of the impairment in daily functioning resulting from the disease. The broader impact of schizophrenia in contrast to that of the somatic diseases, seems to result from the negative social reactions and the economic deprivation often associated with this type of mental illness. Copyright © 2001 John Wiley & Sons, Ltd.