A study was performed to define the normal range of values for anorectal manometry. Normal volunteers were divided according to gender and parity. There were 20 males, 21 nulliparous females, and 18 multiparous females among the 59 subjects. Anorectal manometry using a radial eight-port catheter was performed during resting and squeezing maneuvers of the anal sphincter. Computerized data analysis and three-dimensional imaging were used to calculate sphincter length at rest and squeeze, mean maximum resting and squeeze pressures, and vector symmetry index. The sphincter length at rest and with squeezing in males was significantly greater compared with the two female groups (P < 0.007). Mean maximum squeeze pressures were also significantly elevated in the male group compared with the female groups (P = 0). Mean maximum resting pressures were significantly higher in nulliparous women than in multiparous women (P = 0.04). However, no difference in resting pressures was found between males and nulliparous females. A comparison of the symmetry of the anal canal revealed no differences among the three groups. Ranges for normal anorectal manometry are definable. Normal ranges are distinct for subgroups of patients, particularly with regard to gender and parity. Patients must be compared with their normal subgroups to correctly identify manometric abnormalities.