Obesity levels in the United Kingdom have risen over the years. Studies from the United States and elsewhere have reported variable outcomes for obese liver transplant recipients in terms of post–liver transplant morbidity, mortality, and graft survival. This study was designed to analyze the impact of the body mass index (BMI) on outcomes following adult liver transplantation. Data from 1994 to 2009 were retrieved from a prospectively maintained database. Patients were stratified into 5 World Health Organization BMI categories: underweight (<18.5 kg/m2), normal weight (18.5-24.9 kg/m2), overweight (25.0-29.9 kg/m2), obese (30.0-34.9 kg/m2), and morbidly obese (≥35.0 kg/m2). The primary outcome was an evaluation of graft and patient survival, and the secondary outcome was an assessment of postoperative morbidity. Bonferroni correction was applied with statistical significance set at P < 0.012. Kaplan-Meier curves were used to study the effects of BMI on graft and patient survival. A total of 1325 patients were included in the study: underweight (n = 47 or 3.5%), normal-weight (n = 643 or 48.5%), overweight (n = 417 or 31.5%), obese (n = 145 or 10.9%), and morbidly obese patients (n = 73 or 5.5%). The rate of postoperative infective complications was significantly higher in the overweight (60.7%, P < 0.01) and obese recipients (65.5%, P < 0.01) versus the normal-weight recipients (50.4%). The morbidly obese patients had a longer mean intensive care unit (ICU) stay than the normal-weight patients (4.7 versus 3.2 days, P = 0.03). The mean hospital stay was longer for the overweight (22.4 days, P < 0.001), obese (21.3 days, P = 0.04), and morbidly obese recipients (22.4 days, P = 0.047) versus the normal-weight recipients (18.0 days). There was no difference in death-censored graft survival or patient survival between the groups. In conclusion, this is the largest and only reported UK series on BMI and outcomes following liver transplantation. Overweight and obese patients have significantly increased morbidity in terms of infective complications after liver transplantation and, consequently, longer ICU and hospital stays. Liver Transpl 19:551–562, 2013. © 2013 AASLD.