Cutaneous manifestations in patients with essential thrombocythemia. In a retrospective study of 268 patients with essential thrombocythemia, related cutaneous manifestations were found in 58 (22%). In 27 cases (10%) the related skin lesions were present at the time of the primary diagnosis of essential thrombocythemia. Hematomas, ecchymoses, petechiae, or purpura occurred in 24 (41%) of the 58 patients. Fifteen patients (26%) had erythromelalgia, in 11 of whom it was the initial complaint. Livedo reticularis, recurrent superficial thrombophlebitis, ischemic complications with gangrene, leg ulcers, or ulcers on the toes were other manifestations. Urticaria occurred in two patients, and Raynaud's phenomenon and necrotizing vasculitis were each observed in one patient. Platelet function may be abnormal, and this was found in 13 of 19 patients studied, 9 of whom had spontaneous platelet aggregation. Knowledge of the cutaneous manifestations in essential thrombocythemia may lead to its earlier detection. Prompt diagnosis of essential thrombocythemia is important because treatment may prevent severe hemorrhagic or thrombotic events. 