A case that exhibits the pathologic features of cutaneous lupus erythematosus and the immunopathologic characteristics of pemphigus erythematosus following myasthenia gravis and thymoma is presented, and the literature pertaining to these disease associations is reviewed. The findings in this case were analyzed with respect to the accepted diagnostic criteria for lupus erythematosus, pemphigus, and pemphigus erythematosus. The pathogenic mechanisms that lead to acantholysis in pemphigus are examined in an attempt to explain why acantholysis did not occur in this case.