A 71-year-old man presented with numerous pruritic seborrheic keratoses, with an eruptive onset over the course of 3 months. At presentation, he was also found to have hypopigmented tumors diffusely scattered throughout his body that were found to be mycosis fungoides on histologic examination. A theory regarding the pathophysiology of the development of eruptive seborrheic keratoses in the presence of mycosis fungoides is briefly discussed and 10 previous case reports of the Leser-Trélat sign in the setting of mycosis fungoides are reviewed.