The association of pemphigus and thymoma has been investigated in a recent personally observed case and data from nineteen further cases published in the literature have been reviewed. From these twenty cases several prominent features emerge. Clinically, pemphigus of Senear-Usher type (pemphigus erythematosus) is most commonly found (11/20 cases). There is a male preponderance (at least 13/20 cases) although associated myasthenia gravis which occurred in thirteen cases was more common in females. Thymoma probably preceded pemphigus in all cases, although this was certain in only nine. Evidence of autoimmunity was marked; in addition to antibodies to intercellular substance, anti-striated muscle antibodies were frequent and antinuclear factor was positive in ten out of twelve cases. The prognosis was usually good although thymectomy was generally ineffective or occasionally seemed to have an adverse effect.