Polycythemia vera and essential thrombocythemia are the most common chronic myeloproliferative neoplasms; their molecular basis has been appreciated only recently and is briefly discussed in this article. Major causes of morbidity and mortality are represented by arterial and venous thrombosis, as well as by evolution to myelofibrosis or transformation to acute leukemia. Therapy is currently aimed at reducing the rate of thrombosis without increasing the risk of hematologic transformation that might be caused by exposure to cytotoxic drugs. A risk-oriented approach is employed for stratifying patients to the most appropriate therapeutic options. However, results of clinical trials with interferon, and the expected effects of novel drugs selectively targeting the abnormal pathways that are involved in the clonal myeloproliferation, are pushing therapeutic goals from disease control only to cure. These different issues, and current recommendations for treatment, will be discussed in the review.