Mycosis fungoides is a rare malignant lymphoma that primarily affects the skin. Lymph node and visceral involvement may follow. The disease is chronic in course, displaying numerous clinical variations. Two cases of mycosis fungoides complicated by the development of cutaneous squamous cell carcinoma will be discussed. One of the two patients developed metastatic squamous cell carcinoma from an initial primary cutaneous lesion. Both patients were treated for long periods with topical nitrogen mustard in addition to systemic therapy. The question of topical nitrogen mustard induction of squamous cell carcinoma is raised.