BACKGROUND: This randomized prospective clinical trial compared the hepatic venous outflow drainage and renal function after conventional with venovenous bypass (n = 15) or piggyback (n = 17) liver transplantation. METHODS: Free hepatic vein pressure (FHVP) and central venous pressure (CVP) measurements were performed after graft reperfusion. Postoperative serum creatinine (Cr) was measured daily on the first week and on the 14th, 21st and 28th postoperative days (PO). The prevalence of acute renal failure (ARF) up to the 28th PO was analyzed by RIFLE-AKIN criteria. A Generalized Estimating Equation (GEE) approach was used for comparison of longitudinal measurements of renal function. RESULTS: FHVP-CVP gradient > 3 mm Hg was observed in 26.7% (4/15) of the patients in the conventional group and in 17.6% (3/17) in the piggyback group (p = 0.68). Median FHVP-CVP gradient was 2 mm Hg (0-8 mmHg) vs. 3 mm Hg (0-7 mm Hg) in conventional and piggyback groups, respectively (p = 0.73). There is no statistically significant difference between the conventional (1/15) and the piggyback (2/17) groups regarding massive ascites development (p = 1.00). GEE estimated marginal mean for Cr was significantly higher in conventional than in piggyback group (2.14 ± 0.26 vs. 1.47 ± 0.15 mg/dL; p = 0.02). The conventional method presented a higher prevalence of severe ARF during the first 28 PO days (OR = 3.207; 95% CI, 1.010 to 10.179; p = 0.048). CONCLUSION: Patients submitted to liver transplantation using conventional or piggyback methods present similar results regarding venous outflow drainage of the graft. Conventional with venovenous bypass technique significantly increases the harm of postoperative renal dysfunction. TRIAL REGISTRATION: ClinicalTrials.gov https://clinicaltrials.gov/ct2/show/NCT01707810.