The clinical course of 141 unselected patients (64 m, 77 f, median age 59) with polycythemia vera (PV), treated during the period 1967 to 1986 was analyzed to study prognostic factors and the correlation between treatment strategies and complication rates. Therapy was performed according to a prospectively defined treatment protocol. Primary control of the disease was achieved by phlebotomy. Marrow suppression by radioactive phosphorus or low dose busulphan was used only as a second-line therapy or to lower high platelet counts. The clinical course of the patients was characterized by a low rate of acute leukemia (4%) and a high rate of thromboembolic complications (40%). Myelofibrosis developed in 17 patients (12%). Median survival of the patents was 9.4 years. The prognostic influence of several parameters at the time of diagnosis was tested: age, sex, spleen size, percentage of blood blasts + promyelocytes, leucocyte count, platelet count, hemoglobin, hematocrit, reticulocyte count and the values of the lactate-dehydrogenase (LDH) and the alkaline neutrophil phosphatase (ANP) all had no significant influence on the length of survival. The prognosis of PV patients with atypical disease presentation at diagnosis was not different from patients with typical disease.