In order to determine the relationship between all forms of pemphigus and malignancy or thymoma, a search of the world literature was carried out. Fifty-nine case reports or isolated citations for pemphigus with malignancies or thymomas were noted, including twenty-one reports published before the histological separation by Lever of pemphigus and bullous pemphigoid in 1953. Of these cases, twenty-six were acceptable for analysis. In approximately 54% of patients surveyed with these associations, the malignancy involved the lymphoid or reticuloendothelial systems. Approximately 48% of the patients with pemphigus and malignancy or thymoma had associated autoimmune diseases. Pemphigus with malignancies or thymomas may be related through some intervening variables such as immuno-suppressive therapy or the antigenic and cross-reacting nature of the primary tumour, or through an immunological consequence of associated autoimmune disease. Although reports of pemphigus and concurrent malignancy or thymoma have appeared sporadically in the literature (Skog, 1964; Beutner et al., 1968; Krain et al., 1973), added impetus to the study of these associations has been provided by the demonstration of the production of pemphigus antibodies by a lymphoid neoplasm (Saikia, 1972). It is generally acknowledged that autoimmune mechanisms play an important though as yet ill-defined role in the pathogenesis of pemphigus (Beutner et al., 1968; Beutner, Chorzelski & Jordon, 1970), of thymomas (Stillman& Baer, 1972; Vetters et al., 1973) and of some malignant tumours (Moragas, Winkelmann & Jordon, 1970; Alexander, 1972; Saikia, 1972). In addition, immunosuppressive therapy employed in the management of patients with pemphigus and other autoimmune diseases has been incriminated as a possible inductive mechanism in the subsequent development of malignancy (Harris, 1971; Lowney, 1972; Krain & Bierman, 1973). Saikia (1973) has suggested that every patient with pemphigus should be investigated as far as is practicable to exclude the possibility of a co-existent malignancy, especially in those cases in which systemic corticosteroid therapy is unsatisfactory in controlling the pemphigus. The purpose of this paper is to review the current literature on the association of pemphigus with malignancy or thymoma and to examine critically the factors involved in these inter-relationships. [ABSTRACT FROM AUTHOR]