(1) Anal fissures are very painful but often heal spontaneously. After eliminating other diagnoses, various treatments can be tried while waiting for fissures to heal: warm seat baths, local anaesthetics, and adequate fibre and fluid intake. (2) Clinical evaluation of glyceryl trinitrate 0.4% ointment, a nitrate derivative, is mainly based on a double-blind trial versus excipient in 193 adults with "chronic" fissures. This trial failed to show a clinically relevant analgesic effect of glyceryl trinitrate 0.4%, with only a 3-mm difference versus the excipient on a 100-mm pain rating scale. In another trial including 229 patients, neither 0.2% nor 0.4% glyceryl trinitrate was more effective on pain than placebo. (3) Another placebo-controlled trial including 304 adults treated for 8 weeks showed no efficacy of various doses of glyceryl trinitrate, versus the excipient, on the healing of anal fissures. (4) The most frequent adverse effect, as expected with a nitrate derivative, is headache, which affects about two-thirds of patients and is severe in 20% of cases. Abrupt-onset hypotension is a risk during concomitant use of other vasodilatory drugs. (5) There are no data on pregnant women exposed to glyceryl trinitrate. (6) In summary, glyceryl trinitrate 0.4% ointment does not reduce the pain linked to chronic anal fissures, but it does carry a risk of sometimes severe headache. It is best to continue using simple, non-aggressive treatments.