The selection of treatment for patients with polycythemia vera (PV) still is the subject of much discussion among hematologists. It is emphasized that important physiologic and pathogenic components of the illness relate not only to the erythroid cell, but also to the megakaryocyte. Both play essential roles in causing complications of the disease. Hematologists agree that the mainstay in treatment remains phlebotomy, a basic pillar of the concept of PRIMUM NON NOCERE. In general, the target levels for the hematocrit have been accepted as