Pleural myelomatous involvement in multiple myeloma (MM) is rare, occurring in less than 1% of cases. We retrospectively studied five cases of patients with MM who developed myelomatous pleural effusions. Three men and 2 women with a mean age of 61 years presented with myelomatous pleural effusion. The pleural fluid electrophoresis revealed a peak of IgG in three cases, of IgA in one case, and of lambda light chains in one case, which were identical to that in the sera of the patients. Detection of typical plasma cells in pleural fluid cytology was contributive, and histologic confirmation by pleural biopsy was positive in four cases. Treatment consisted of chemotherapy. The clinical outcome was initially good, but relapses occurred in all cases early and were complicated by fatal infections. Myelomatous pleural effusion is a rare affection. It is usually a late complication associated with poor prognosis.