The clinical characteristics of aquagenic pruritus (AP) based on a series of thirty-six patients are presented. AP is characterized by the development of severe, prickling-like skin discomfort that is without observable skin lesions and that is evoked by contact with water at any temperature. Other causes of pruritus associated with water contact must be excluded. In the thirty-six patients, skin discomfort developed within minutes of water contact in approximately half. In others, discomfort began 2 to 15 minutes after water exposure had ceased. The pruritus was usually generalized, lasting from 10 to 120 minutes (average, 40.6 minutes), and in 55% was associated with symptoms of acute emotional lability, There was no increased prevalence of atopy. Thirty-three percent reported a family history of water-related itching. Of fourteen patients treated with ultraviolet B phototherapy, eight (57%) noted significant relief. Of thirty-four patients, sixteen (47%) noted partial relief with oral antihistamine therapy. Patients with polycythemia rubra vera (PRV) may present with symptoms similar to those of AP, and all patients with symptoms consistent with AP should be investigated for the presence of PRV.