A patient with primary biliary cirrhosis (PBC) who developed idiopathic myelofibrosis (IM) is reported. The initial diagnosis of PBC was established by liver biopsy, performed after a 2-month history of constitutional symptoms associated with abnormalities of the serum liver enzymes, with typical serum immunological markers being found. Although a favorable response of PBC to prednisone was observed, one and a half year later the patient developed anemia with anisocytosis and poikilocytosis, tear-drop cells, and leukoerythroblastic picture, and IM was diagnosed by bone marrow biopsy. A few months later, a rapid worsening of the patient's clinical condition was noted, with an increase in the constitutional symptoms and need for frequent packed RBC transfusions, and she finally died from an infectious complication. This case represents a new association of IM with an autoimmune disease, supporting the hypothesis of a possible immune basis of IM in some cases.