The clinical importance of congestion of the remnant right lobe has not yet been fully elucidated in donors who donate their left lobe with the middle hepatic vein. The impact of congestion on clinical course and liver regeneration in 52 donor remnant livers were evaluated. The donors were divided into three groups according to the degree of the congestion: the mild [congestion ratio (CR) < 10%], moderate (CR ranged from 10% to 25%) and severe congestion groups (CR > 25%). The regeneration ratio of the graft at postoperative day 7 (7 POD) was 22.0 +/- 14.3% and inversely correlated with the CR in the remnant right lobe (P = 0.003). Aspartate aminotransferase and alanine aminotransferase at 7 POD were significantly higher in the severe CR group in comparison to the mild CR group (P = 0.003 and 0.019, respectively), but those of the three groups were comparable at 30 POD. The hospital stays were significantly longer in the severe CR group (P = 0.010). In conclusion, the congestion of the donors' remnant right liver can lead the transient liver dysfunction and poor regeneration. Therefore, the conversion of the graft from the left to right lobe might be appropriate according to the degree of the congestion.