Botulinum toxin can chemically denervate striated muscle. Botulinum toxin A (15 U) was used to treat ten patients with chronic anal fissure by injection in the internal sphincter. In seven patients, the lesion healed at 2 months after treatment; one relapsed at 3 months. In one patient the lesion healed at 1 month, but partly relapsed a month later. Mild faecal incontinence lasting for 1 day was observed in one patient. We propose that botulinum toxin injections in the internal anal sphincter be considered an alternative approach to surgical therapy of anal fissure.