[Polycythemias of young subjects (author's transl)].

During the last 12 years, 86 apparently primary polycythemias have been observed in subjects less than 40 years old. In twelve of them a non-suspected cause has been found (seven abnormalities of the hemoglobin function). In 43 cases, all males, the erythrocytosis (red cell volume more than 36 ml/kg) was pure and stable, without any complication; this "benign erythrocytosis" probably depicts extreme values of the normal distribution of the red cell mass. In 31 cases, the disease had criteria similar to those of polycythemia vera observed in older patients; in 12 of these cases, severe thrombo-embolic complications have been observed at the very beginning of the disease; however no further complication has been seen, when the patients were actively treated (phlebotomies or 32P); at the present time, no one of these cases did show transformation into acute leukemia, but the long-term prognosis (beyond 15 years) cannot yet been precisely drawn.