The role of nephrologists as de facto primary care providers (PCP) for dialysis patients is of increasing interest. We sought to determine the proportion of patients who rely on nephrologists for primary care and to identify demographic variables associated with this primary care responsibility. We reviewed the charts of 158 patients receiving hemodialysis at a suburban, freestanding, teaching hospital affiliated outpatient unit from December 1999 through January 2001. In addition, each patient was interviewed and completed a survey. Non-nephrologists were considered to be a patient's PCP if there was chart, survey or interview evidence of such a relationship. Of the 158 patients, only 56 patients had a PCP. The nephrologist thus was the de facto PCP in 65% of hemodialysis patients, a responsibility that was 3.3-fold more likely for patients not enrolled in a health maintenance organization (HMO) or managed care organization (MCO). In the non-HMO/MCO group, patients with a PCP had been on dialysis for less time than those without a PCP [2.7 vs. 4.6 years (P=0.0006)]. Only 32% of patients on dialysis <1 year had nephrologists as de facto PCP vs. 71% of those on dialysis more than 1 year (P=0.0002). This association between time on dialysis and de facto use of nephrologists as PCP was not accounted for by the shorter time on dialysis of HMO/MCO enrollees. The extent to which the nephrologist fulfills the often unsought role as PCP needs further investigation.