We evaluated the maxium static pressure and extent of high pressure in the anal canals of 6 males and 6 females with a mean age of 2.9 years. The sample included 11 patients with hard stool or anal membrane stenosis who were later cured by conservative therapy within 2 months, and one 6 year old boy with a chronic anal fissure later cured by operative therapy. Maximum static pressure and the length of the anal canal in children having high pressure were measured using an open-tip manometer with a continuous infusion system. Values for maximum static pressure for all 12 patients are expressed as a percentage of the values obtained from aged-matched controls reported in the literature. Values for 11 patients were observed to be 101 ±7.1%, and the value for the 6 year old boy was observed to be 125%. The length of the anal canal in children who had high pressure was 2.1±0.5cm, similar to the 2.2cm found on the normal control group. Adult patients with anal fissure have high pressure due to abnormal activity of the internal sphincter. In treatable cases in infants and children, the anal canal pressure was normal. Apparently the cause of anal fissure is trauma caused by hard stools and anal membrane stenosis.