The dialytic therapy of choice in critically ill patients with acute renal failure (ARF) is a matter of controversy. The clinical outcome of such patients managed with either conventional dialytic therapy (CDT) or acute continuous hemodiafiltration (ACHD) was compared through retrospective review of medical records from the intensive care unit of a tertiary institution. Records from 167 critically ill patients with ARF consecutively treated in the same intensive care unit were reviewed. Eighty-four patients with ARF treated by CDT were compared to 83 treated with ACHD. The etiology of ARF and the degree of illness severity were similar in both groups (failing organs: CDT 3.9 vs. ACHD 4.1; mean APACHE II score: CDT 25.8 vs. ACHD 28.1). Overall survival was 29.8% for the CDT patients and 41% for the ACHD group (NS). In those with two to four failing organs, survival was greater in the ACHD group (53.8% vs. 31.1%; p < 0.025). This was also true for patients with an intermediate APACHE II score (24-29) who demonstrated better survival when treated by ACHD (46.4% vs. 12.5%; p < 0.025). Acute continuous hemodiafiltration was associated with better control of azotemia and hyperphosphatemia and increased nutritional intake. This retrospective study suggests that ACHD may offer clinically significant advantages over CDT, particularly in patients with an intermediate degree of critical illness severity.