For many cancers, features of the metabolic syndrome, such as diabetes and obesity, have been associated with both increased risk of cancer development and poor outcomes. We examined a large retrospective cohort of 342 consecutive patients who underwent liver transplantation for hepatocellular carcinoma between January 1999 and July 2010 at our institution. We evaluated the relationship between diabetes, obesity, hepatocellular carcinoma (HCC) recurrence, and overall survival. We found that a body mass index (BMI) higher than 30 was an independent predictor of poor overall survival in a multivariable Cox model, approximately doubling the risk of death after transplantation. A BMI higher than 30 was also a predictor of recurrent HCC, although this was of borderline statistical significance (hazard ratio for recurrence, 1.9; 95% confidence interval, 0.9-4.1). We also found increased BMI to be an independent predictor of microvascular invasion within HCC tumors, lending a possible explanation to these results. Those with diabetes showed worsened overall survival compared with those without diabetes in univariate but not multivariable analysis, possibly related to longer wait times. Our findings suggest a relationship between higher BMI, tumor vascular invasion, increased recurrence, and worsened overall survival. These findings may help explain why those with high BMI have worse outcomes from their cancers. A better understanding of the role of obesity and diabetes in patients with cancer should help develop better predictors of outcome and improved treatment options for patients with HCC.