||BACKGROUND & AIMS: Studies of liver cancer risk in recipients of solid organ transplants generally have been small, yielding mixed results, and little is known about biliary tract cancers among transplant recipients. METHODS: We identified incident hepatobiliary cancers among 201,549 US recipients of solid organs, from 1987 through 2008, by linking data from the US transplant registry with 15 cancer registries. We calculated standardized incidence ratios (SIRs), comparing risk relative to the general population. We also calculated incidence rate ratios (RRs), comparing risk for hepatocellular carcinoma (HCC) and total (intrahepatic and extrahepatic) cholangiocarcinoma among subgroups of recipients. RESULTS: Of transplant recipients, 165 developed hepatobiliary cancers (SIR, 1.2; 95% confidence interval [CI], 1.0-1.4). HCC risk was increased among liver recipients (SIR, 1.5; 95% CI, 1.0-2.2), especially 5 or more years after transplant (SIR, 1.8; 95% CI, 1.0-3.0). Cholangiocarcinoma was increased among liver (SIR, 2.9; 95% CI, 1.6-4.8) and kidney recipients (SIR, 2.1; 95% CI, 1.3-3.1). HCC was associated with hepatitis B virus (RR, 3.2; 95% CI, 1.3-6.9), hepatitis C virus (RR, 10; 95% CI, 5.9-16.9), and non-insulin-dependent diabetes (RR, 2.5; 95% CI, 1.2-4.8). Cholangiocarcinoma was associated with azathioprine maintenance therapy (RR, 2.0; 95% CI, 1.1-3.7). Among liver recipients, primary sclerosing cholangitis was associated with an increased risk of cholangiocarcinoma, compared with the general population (SIR, 21; 95% CI, 8.2-42) and compared with liver recipients without primary sclerosing cholangitis (RR, 12.3; 95% CI, 4.1-36.4). CONCLUSIONS: Risks for liver and biliary tract cancer are increased among organ transplant recipients. Risk factors for these cancers include medical conditions and potentially medications taken by recipients.