Psoriasis vulgaris is occasionally accompanied by autoimmune bullous diseases, but the opposite is very rare. We document here the first reported case of generalized pustular psoriasis that appeared during steroid therapy for bullous pemphigoid. The serum cytokine levels and the results of an immunohistochemical study over the disease course suggest that the immunological state was consistent with a shift from Th2-dominance to Th1-dominance. IL-17-producing cells appeared in the skin lesions when each disease was most exacerbated and disappeared after remission. Thus, the present case demonstrated a dynamic immunological state in which the appearances of Th1 and Th2 as well as Th17 varied during the course of the disease.