The progressive shortage of liver donors has mandated investigation of living-donor transplantation (LDT). Concerns about increasing risk to the donor are evident, but the impact of the degree of parenchymal loss has not been quantified. We analyzed clinical and biological variables in 45 LDT performed by our team over 2years to assess risks faced in adult LDT. All donors are alive and well with complete follow-up through to February 2001. When the three operations were compared, right hepatectomy (RH) was significantly longer in terms of anesthesia time and blood loss compared with left hepatectomy (LH) and left lobectomy (LL). Donor remnant liver was significantly reduced after RH compared with LH and LL. There were significant functional differences as a consequence of the remnant size, measured by an increase in peak prothrombin time after RH. RH for adults represents a markedly different insult from pediatric donations in terms of parenchymal loss and early functional impairment. Left hepatectomy donation offers modest advantage over right lobes but seems to confer substantial technical risk for a small gain in graft size. Unless novel strategies are developed to enhance liver function of the LH graft in the adult recipient, right lobe donation will be necessary for adult LDT.