Topical chlormethine has been widely used in the early stages of mycosis fungoides for many years. Cutaneous reactions (skin irritation and itch) are the most frequent adverse effects. Herein we report a rare side effect: severe necrotic leg ulcers.An 82-year-old woman with a history of high blood pressure developed hyperalgesic necrotic ulcers on the lower limbs following local trauma one month after initiation of topical chlormethine (Valchlor®) to treat mycosis fungoides. Aetiological examination showed moderate peripheral arterial disease which, while constituting an aggravating factor, did not account fully for these skin ulcers. Moreover, drug-induced ulcer was suspected on account of the chronology. Dermal corticoids and topical treatment were prescribed in place of chlormethine and led to a favourable outcome.Incrimination of chlormethine was based on the chronological and semiological criteria. This is the first published case of leg ulceration induced by Valchlor®.