Specific treatments for mycosis fungoides, including electron beam irradiation, topical mechlorethamine, and psoralen plus ultraviolet A (PUVA) may be associated with the development of skin cancers after a variable latency period. Because these treatments are often not curative, topical therapies for mycosis fungoides, administered sequentially or concomitantly, are being used increasingly in order to control recurrent disease. This report documents the development of multiple cutaneous tumors, including squamous cell carcinoma, basal cell carcinoma, actinic keratoses, keratoacanthomas, and one case of lentigo maligna, in seven patients who received topical therapies for mycosis fungoides. In contrast to the usual latency period between ionizing radiation therapy and the development of skin cancer, two of our patients who had received prior PUVA therapy developed multiple skin tumors upon completion of electron beam irradiation. The development of metastatic squamous cell carcinoma in two of the other seven patients with multiple cutaneous neoplasms suggests that this potential hazard must be considered in the evaluation and treatment of patients with mycosis fungoides.