Since 1973, more than 75 patients with hypocomplementemic urticarial vasculitis syndrome (HUVS) were reported, but valvular heart disease does not seem to have been noted in these patients. Since 1993, however, five patients with HUVS accompanied by Jaccoud's arthropathy (JA) were found to have serious valvular heart disease. To characterize the cardiac valvulopathy of the third patient with HUVS/JA to have undergone valve replacement, this study included the use of routine and special tissue stains, as well as immunohistochemical staining. We compared gross and histologic findings of this patient's valve to those of two other patients with this complex syndrome who underwent valve replacement. Pathologic findings of these latter two patients were described in separate earlier reports. Histologic examination of the resected valves in all three patients showed an acute necrotizing endocarditis and fibrin deposition on the surface of valve leaflets. Beneath the surfaces of the leaflets, there was evidence of chronic inflammation, consisting of lymphocytes and histiocytes. A fibrocalcific degenerative change was also present in all three valves. Positive staining for IgG, IgA, IgM, and light-chain determinant-bearing proteins was detected primarily at the valve surface in special studies of the aortic valve of the patient described in the current report. Patients with HUVS and associated JA should be evaluated for the presence of valvular heart disease. The latter is probably a nonrheumatic, inflammatory, and degenerative process, mediated by immune complex, as well as cellular immune mechanisms.