Leukemic transformation of chronic idiopathic myelofibrosis (CIMF) to acute lymphoblastic leukemia (ALL) is rare. We report a case of a patient with CIMF who developed paroxysmal nocturnal hemoglobinuria (PNH) 2 years after initial presentation. His disease eventually transformed to ALL of precursor B-cell type. In that CIMF and PNH are clonal stem cell disorders with different pathogeneses, there may be an association between them. However, leukemic transformation is a rare sequel of both disorders. Coexistence of CIMF and PNH and subsequent transformation to ALL have, to our knowledge, never been previously reported in the world literature. The simultaneous presentation of CIMF and PNH, complicated by the rare sequela of leukemic transformation, raises important issues with regard to diagnosis and treatment.