Background.Waiting time to liver transplantation (LTx) has dramatically lengthened, but the proportion of candidates who die awaiting transplantation has not increased. We evaluated whether longer waiting time for LTx candidates increases mortality.Methods.A cohort of candidates listed for LTx between 1990 and 1993 by three large transplantation programs was followed for 2 years. The exposure measure was ABO blood type, which is not inherently related to outcome, but is a major determinant of waiting time. The main outcome measure was 2-year mortality, as evaluated by logistic regression analysis that controlled for differences in clinical status at the time of evaluation for LTx.Results.The 308 candidates with type O blood waited longer for LTx (median 109 days) than the 399 candidates with other blood types (median 58 days)(P=0.001). Candidates listed for LTx with type O blood had better clinical status at evaluation, but then had higher pretransplantation mortality (13.3%) than other candidates (7.0%)(P=0.005). Blood group O candidates had higher 2-year mortality (26.6%) than other candidates (22.1%), which on multivariate analysis resulted in a mortality odds ratio at 2 years of 1.52 (95% confidence interval=1.04-2.23). With the difference in median waiting time between blood groups increasing from 44 days in the first year to 108 days in the third year, the 2-year mortality odds ratio also rose from 0.94 to 1.97.Conclusions.When compared with LTx candidates with other blood types, blood type O candidates have longer waiting times and higher pretransplantation mortality, which results in higher 2-year mortality.