Acute renal failure (ARF) is a common and severe complication after liver transplantation (LT). The aim of this study was to ascertain the impact of ARF requiring dialysis in the outcome of LT and to analyze the risk factors leading to this event in the early post-operative period. From October 1988 to December 1994, 172 LT were performed in 158 patients. Postoperative ARF occurred in 88 transplants (51.1%) during the early postoperative period: mild ARF was found in 46 (serum creatinine 1.5-3 mg/dl), moderate ARF in 12 (serum creatinine > 3 mg/dl) and severe ARF in 30 (serum creatinine > 3 mg/dl with dialysis requirement). Preoperative, intraoperative, and postoperative variables were studied, comparing patients presenting severe ARF with the remaining patients. Postoperative mortality in the dialysed group was much higher than in the non-dialysis group (50% vs. 13.4%)(p < 0.001) and 1-yr actuarial graft survival was 73.4% for the non-dialysed group compared with 40.9% for the dialysed group (p < 0.05). Among 38 variables investigated, only two factors had independent prognostic value in multivariate analysis: preoperative serum creatinine > 1.5 mg/dl (OR = 4.4, p = 0.006) and graft dysfunction grades III-IV (OR = 8.9, p = 0.001). In conclusion, ARF is a severe complication post-LT; its appearance could be predicted in patients with pre-transplant renal dysfunction, severe graft dysfunction, or both. However, in many cases renal function may revert to normal if treated aggressively with early dialysis support.