The article presents discussion of basic hypotheses of pathogenesis of primary sclerosing cholangitis (PSC): genetically conditioned pathology, autoimmune pathology, result of inflammatory reaction in bile ducts, cholangiopathy. The authors presents a clinical case of monozygotic twins with association of PSC and nonspecific ulcerative colitis (NUC). The first twin had a severe course of PSC and mild course of NUC; he died due to bacterial complications of cholangitis. The second twin--patient B--had an opposite situation: severe course of NUC, while PSC was suspected only after determination of cholestasis biochemical markers. As soon as cholestasis was revealed, patients B was treated with Ursofalk and Budenofalk (2001). He received Salofalk as a remedy of basic therapy for NUC. Repeated liver biopsy (2005) showed no progression of PSC, but there were present minimal biochemical signs of cholestasis. So, it is necessary to investigate the first degree relatives of patients with PSC. The timely administered treatment in some cases gives the possibility of the control of the disease course.