There is lack of agreement as to whether or not psoriasis may precede mycosis fungoides. Monographs and textbooks state that psoriasiform lesions may be prodromata of mycosis fungoides (1), that an eruption resembling psoriasis may occur in the early stages (2), and that mycosis fungoides may begin with lesions indistinguishable from psoriasis (3). Herxheimer and Martin said that “in a great number of cases the initial efflorescences of mycosis fungoides are morphologically so identical with psoriasis vulgaris that the diagnosis of psoriasis is made even in the presence of nodes and tumors because of the spectacular morphological analogy of the scaling lesions” (4). Indeed, there is almost universal agreement that pre-fungoid lesions often resemble psoriasis (5), and most authors include psoriasis in the differential diagnosis of premycotic eruptions. There are three schools of thought at present: 1) that psoriasiform premycotic lesions actually represent mycosis fungoides in its prefungoid stage no matter how closely they resemble psoriasis clinically or histologically (6); 2) that mycosis fungoides and psoriasis may exist simultaneously in the same person as separate diseases (7); or 3) that psoriasis may develop into mycosis fungoides (8). Berggreen recently discussed this difference of opinion but mistakenly concluded that “it is impossible to differentiate the two diseases clinically or even histologically” (7a).