Fistula-in-ano in infants is thought to begin with a cryptitis that proceeds to a perianal abscess. Of 52 patients in 15 years, 51 were male, 45 were under 12 months, 7 had multiple tracts, and 2 recurred in 6 years; all of which points to a developmental anomaly. We believe the anomaly to be a markedly irregular thickened dentate line that harbors from 3 to 13 deep (3 to 10 mm) abnormal crypts (AC), which foster cryptitis. There have been no recurrences since we started doing cryptotomies on these AC in addition to the fistulotomy. The cause may be a defect in the dorsal portion of the cloacal membrane which fuses with the hindgut during the seventh week.