Mycosis fungoides is the most common subtype of primary cutaneous lymphoma and has several clinical variants. We report a 74-year-old man presenting with an acquired palmoplantar keratoderma initially diagnosed and treated as psoriasis with suboptimal improvement. Several months later the patient developed patches and plaques that were histologically consistent with mycosis fungoides. These lesions were ameliorated with the treatment of the underlying mycosis fungoides and the palmoplantar keratoderma resolved promptly with radiotherapy. This case highlights the importance of considering mycosis fungoides as an infrequent but serious cause of acquired palmoplantar keratoderma.