A considerable number of reports have documented mycosis fungoides (MF) mimicking other dermatoses, but a comprehensive review has not been published. Our aim was to comprehensively review reports of various dermatoses simulated by MF. Additionally, 2 cases in which MF simulated diseases not previously documented (psoriasis and erythema annulare centrifugum) are presented. A literature search of all case reports of MF cited in the MEDLINE database from 1966 through 2000 plus those in one of the author's (H. Z.) files was performed. A total of 23 reported cases of dermatoses mimicked by MF were found. With the additional 2 dermatoses now presented, this yields a total of at least 25 diseases that can be simulated by MF. In view of the considerable number of dermatoses simulated by MF, the term the great imitator is appropriate for MF. (J Am Acad Dermatol 2002;47:914-8.)