The authors report a case of urticaria pigmentosa with systemic mastocytosis and review the literature on this occasion. The onset of the disease was marked by the development of ascites. Ascites is rarely mentioned in this affection and remains, as with other manifestations of systemic mastocytosis, without any explanation. The diagnosis was established first on the diffuse mastocyte-infiltration especially in the bone-marrow and second, on the hypersecretion of hormonal factors especially histamine by mastocytes. The symptomatic treatment of this affection is based on histamine inhibitors and disodium cromoglycate seems to be an efficient drug. With the possible development of acute leukemia, the eventual association with a carcinoma and the frequency of serious digestive bleeding, the prognosis may be very poor.