FIC1 disease collectively refers to a group of autosomal-recessive familial liver disorders characterized by intrahepatic cholestasis due to mutations in the ATP8B1 gene (initially named FIC1). Classically, FIC1 disease comprises two different disorders: progressive familial intrahepatic cholestasis type 1 (PFIC1) and benign recurrent intrahepatic cholestasis (BRIC). However, we now view these two disorders as two ends of a continuum. Current therapeutic strategies for FIC1 disease, both medical and surgical, may relieve symptoms, but are presently insufficiently evaluated. ATP8B1 encodes a protein belonging to a recently defined subfamily of P-type ATPases. The biochemical and cellular functions of its product, FIC1, and the mechanisms by which its absence or dysfunction leads to cholestasis are currently elusive. Further studies to elucidate FIC1's function will be essential to unravel the pathogenesis of FIC1 disease. Such studies will also have a general impact on our understanding of the molecular mechanisms of bile formation and may therefore improve clinical management of both hereditary and acquired forms of cholestasis.