The percent distribution of selected comorbid conditions from a national sample of 3,399 Medicare patients starting maintenance hemodialysis in 1986-87 is described. Using the Cox proportional hazards model, the relative mortality risk (RR) was assessed for comorbid conditions at time of ESRD while adjusting for the other comorbid and demographic covariates. Coronary artery disease and congestive heart failure, each present in 41 percent of patients, were associated with RR of 1.22 and 1.26 respectively (p < 0.0005 each). Fifty percent of patients had a serum albumin concentration at onset of ESRD of less than 3.5 gm/dl, and an increased risk of dying. Additionally, patients recorded as undernourished had an elevated risk (RR = 1.34, without adjustment for serum albumin, p < 0.0001). Other factors associated with a statistically significant increased mortality risk (p < 0.005) included older age, diabetes as cause of ESRD (particularly if insulin dependent), history of neoplasm, active smoker, and relatively low serum creatinine concentration. By describing the magnitude of risk associated with comorbid conditions, this study emphasizes the need for preventive efforts during the pre-ESRD stages of renal impairment. Studies are needed to document whether improvement in serum albumin or other comorbid factors before ESRD leads to reduction in mortality risk for ESRD patients.