OBJECTIVE:Conventional hemodialysis (HD) predominates over peritoneal dialysis (PD) around the world. Prospective and comparative studies comparing the costs of these modalities are scarce. In the present prospective assessment, we describe the resources used and total patient costs for both HD and PD. ♢ METHODOLOGY:We assessed 249 patients on HD and 228 on PD. All patients were 18 years of age or older and on stable dialysis. The information was collected at three points over 1 year, using standard questionnaires. The sources for costs were the Brazilian public and private health care systems. Societal perspective was considered. ♢ STATISTICAL ANALYSIS:Core trends and dispersions were measured. Regression models assessed the impact of modality on the average total cost per patient per year. ♢ RESULTS:Of the 249 HD patients and 228 PD dialysis patients, 189 (74%) and 160 (70%) respectively completed follow-up. The mean age for women was 55.8 years; for men, it was 59.8 years (p = 0.001). The average total cost per patient-year was US$28 570 for HD and US$27 158 for PD. By category, the costs consisted of direct medical-hospital costs (82.3% for HD, 86.5% for PD), direct nonmedical costs (5.3% for HD, 3.7% for PD), and indirect costs (12.4% for HD, 9.8% for PD). Overall costs were less for PD patients than for their HD counterparts (p = 0.025). ♢ CONCLUSIONS:Maintenance dialysis represented the most important source of costs for both modalities; loss of productivity incurred significant costs. Future studies should contemplate the social consequences arising from each modality.