Scleromyxedema is a rare fibromucinous connective tissue disorder characterized by papular skin lesions associated with sclerosis and a serum monoclonal gammopathy. Little is known about either the natural history or the systemic manifestations of this disease. We reviewed the medical records of 19 patients with biopsy-proven scleromyxedema seen from 1950 to 1985 for evidence of systemic disease. There were 10 males and 9 females with a median age at diagnosis of 53 years. Monoclonal gammopathy was present in 13 patients. Eight patients complained of dysphagia; 3 had proximal esophageal dysfunction and 1 had total esophageal aperistalsis on barium swallow. Proximal muscle weakness was noted in 5, with an inflammatory myopathy in 3. Six patients complained of dyspnea on exertion. Of these, 5 had reduced diffusing capacity, 3 had reduced volumes, and 2 developed cor pulmonale. Pathologic changes characteristic of "scleroderma kidney" were demonstrated in 1 patient at postmortem. One patient had Raynaud's phenomenon and 2 had arthralgias/arthritis with noninflammatory synovial fluids. Although 8 of 12 patients treated with melphalan noted regression of their skin changes, no consistent improvement in the extracutaneous manifestations was demonstrated. Furthermore, 2 patients died of sepsis related to melphalan-induced myelosuppression, and 4 developed hematological malignancies following melphalan therapy. In conclusion, systemic manifestations in scleromyxedema are more prevalent than previously recognized, and can resemble those of scleroderma. Significant toxicity occurred with the use of alkylating agents in these patients, with treatment-related complications developing in 45% of patients treated with melphalan. The lack of definitive data regarding the natural history of this disease complicates the question of optimal therapy, but the use of alkylating agents should be reserved for those patients with severe debilitating skin disease.