Polycythemia vera (PV) and essential thrombocythemia (ET) are associated with life-threatening thrombohemorrhagic events, and disease progression and development of non-hematological malignancies also reduce long-term survival. We retrospectively surveyed thrombohemorrhagic events and overall survival (OS) in 62 PV and 117 ET patients. The cumulative incidences of thrombohemorrhagic events in PV and ET patients were 11.3 and 10.3%, and the incidence rates were 2.42 and 1.85 per 100 person-years. The combined incidence rates of disease progression and development of non-hematological malignancies in PV and ET patients were 1.73 and 1.69 per 100 person-years. The incidence rates of thrombohemorrhagic events in our Japanese PV/ET patients were lower than those reported by most Western studies, but were comparable to those in the largest prospective observational study in ET patients. The combined incidence rates of disease progression and development of non-hematological malignancies were similar between Japanese and Western PV/ET patients. In ET patients, the conventional risk stratification model based on the presence of advanced age or history of thrombosis was useful to predict thrombosis risk, and both the conventional model and the International Prognostic Score of thrombosis in ET based on the above 2 risk factors plus increased leukocyte count could predict poor survival.