Most studies of stress and coping processes among patients with serious illnesses have focused on acute illness states. Far less research has involved systematic examination of the types and frequency of illness-related stresses experienced by individuals living with chronic illness. To compare the nature and degree of illness-related stress posed by four chronic diseases, reports of illness stress were obtained from 170 middle-aged and elderly outpatients faced with a diagnosis of cancer, rheumatoid arthritis, diabetes mellitus, or hypertension. The results revealed that the two most frequently named stresses were demands imposed by the treatment regimen and restrictions imposed on the patient's lifestyle. Other important concerns reported were coping with pain and disease-related symptoms, limited mobility, and problems with social relationships caused by the illness. The results indicated that although a set of stresses common to chronic disease could be empirically identified, important illness-to-illness differences existed in the type and intensity of stress reported. Cancer patients expressed fears of death, uncertainty about future health, interpersonal relationship problems, and disease-related symptoms; diabetics felt stressed by treatment demands, and arthritics were concerned with physical limitations. While these findings conform to objective clinical features of each diagnosis, they also emphasize the importance of attending to patients' subjective illness experiences in providing comprehensive medical care. (Author/NRB)