The authors measured the length of the surgical anal canal (anorectal ring to anal verge) in 108 men and 103 women; the age ranged from 18 to 90 years (average 59 years). The average length of the surgical anal canal was 4.2 cm (range 3.0-5.3 cm). In men the average length was 4.4 cm (range 3.2-5.3 cm) compared with the average length of 4.9 cm (range 3.0-5.0 cm) in women (P less than 0.001). The average length of the anatomic anal canal (dentate line to anal verge) was 2.1 cm (range 1.0-3.8 cm). In men, the average length was 2.2 cm (range 1.4-3.8 cm), whereas in women the average length was 2.0 cm (range 1.0-3.2 cm) (P less than .01). The length of the anatomic anal canal has no relationship to the length of the surgical anal canal or vice versa (P less than 0.1). There was no statistically significant difference in the length of the surgical anal canal or the anatomic anal canal in persons below 60 years old versus those above in either sex (P greater than 0.01).