The review of the pertinent literature disclosed 36 reports of familial multiple myeloma, described mostly in siblings, to which the authors add one more family. These patients did not differ significantly from those with non-familial myeloma with regard to sex, age, distribution of monoclonal proteins, clinical and laboratory data, and the course and prognosis of the disease. An increased incidence of immunoglobulin abnormalities was observed in healthy relatives of patients affected with familial myeloma. In most cases the time interval of the diagnosis of myeloma in a family member of a known patient was under 4 years. These observations, in conjunction with reports of myeloma occurring in clusters in a community and the appearance of myeloma in spouses raise the possibility of an environmental factor (virus?) which may contribute to the pathogenesis of myeloma in genetically predisposed individuals. Multiple myeloma should be added to the list of neoplastic diseases in which the family history is relevant and in which genetic and possibly environmental factors may be pathogenetically involved.