The Italian Society of Nephrology (SIN) promoted a census of the renal and dialysis units to analyze structural and human resources, organizational aspects, activities and epidemiological data. An online 158-item questionnaire for the year 2004 was used. Three hundred sixty-three public renal units, 303 satellite dialysis centers and 295 private dialysis centers were identified, resulting in a total of 961 dialysis centers (16.4 per million population, pmp). The inpatient renal beds were 2,742 (47 pmp). Renal and dialysis activity was performed by 3,728 physicians (64 pmp), of whom 2,964 (80%) were nephrologists. There was no permanent medical assistance in 41% of the satellite dialysis centers. Renal admissions (1,800 pmp) and renal biopsies (99 pmp) were done. The management of the acute renal failure was one of the most relevant activities in the public renal units (13,456 cases, 230 pmp). In 2004 9,858 new cases of end-stage renal disease (169 pmp) were diagnosed. On December 31st 2004, 43,293 patients (741 pmp) were on renal replacement therapy, of whom 89.7% on hemodialysis and 10.3% on peritoneal dialysis. Renal transplant recipients were 16,765 (287 pmp). The benchmark data derived from this census show interesting comparisons between centers, regions and groups of regions. These data realised the clinical management of renal disease in Italy.