A randomized clinical trial assessed the value of regular anal dilatation in combination with a topical local anaesthetic in the treatment of 82 patients with a posterior fissure-in-ano. One month after treatment the fissure had healed in 43.6 per cent of patients using 2 per cent lignocaine gel alone and in 41.9 per cent of patients who also used a St Mark's Hospital anal dilator. Thus the regular use of such a dilator did not contribute to the success of conservative therapy in patients with a posterior anal fissure. A review of patients who presented with anterior or lateral anal fissures during the trial period revealed that healing was achieved in 73.3 per cent of patients without operation within 1 month of diagnosis.