The causes, extent, and quantification of depression in end-stage renal disease (ESRD) patients have been a concern of psychologists and physicians. To assess depression and its possible causes, 57 patients with ESRD treated with hemodialysis (HD, n = 43) or continuous ambulatory peritoneal dialysis (CAPD, n = 14) and 16 patients with chronic renal insufficiency (CRI) were interviewed and completed the Beck Depression Inventory (BDI) and the Illness Effects Questionnaire (IEQ). An ESRD severity coefficient was used to measure chronic illness severity in the patients treated with dialysis, and blood urea nitrogen (BUN) and creatinine levels were used to assess severity of renal disease and adequacy of treatment. A cognitive item subset of the BDI (CDI) was used as a measure of depression. When patients treated with HD and CAPD were compared, CAPD patients were younger, had a shorter duration of dialysis treatment, and less severe medical illness, but the groups did not differ on the IEQ, BDI, or CDI. The IEQ did not correlate with age or disease variables. Both the CDI and the total BDI scores correlated with the IEQ. Perception of illness (IEQ) correlated significantly with cognitive depression for the CAPD and HD patients. For CAPD patients only, a significant correlation between the IEQ and severity of medical illness was obtained. Perception of illness and creatinine concentration were strongly correlated with cognitive depression in the patients with CRI as well. For all renal patients, level of depression was more strongly related to perception of illness than physical illness variables.(ABSTRACT TRUNCATED AT 250 WORDS)