Large-scale whole-genome sequencing of the Icelandic population identified an association between several mutations of ABCB4 encoding the hepatobiliary phosphatiylcholine floppase with liver diseases and function in the general population. Whereas rare mutations of this transporter were known to cause progressive familial intrahepatic cholestasis, the genome-wide association studies in Iceland find the common ABCB4 variant c.711A>T to be a general risk factor for elevated aminotransferases and higher impact variants to be potential determinants of early-onset gallstone disease, cholestasis of pregnancy, liver cirrhosis, and hepatobiliary cancer.