PURPOSE: We assessed the nature of the ultraslow wave in patients with hemorrhoids and chronic anal fissure according to clinical findings and manometry in this study. METHODS: Three hundred and thirty-three patients with hemorrhoids and 88 patients with chronic anal fissure were included. Anorectal manometry was performed according to a modified protocol based on the Coller's study. The ultraslow wave was determined as an undulating wave equal or less than two waves/min. RESULTS: The ultraslow wave was found in 142 of the 333 patients (42.6%) with hemorrhoids and 44 of the 88 patients (50%) with chronic anal fissure. The pressure variables (maximal resting and squeeze pressure, rectal pressure at the beginning of rectoanal inhibitory reflex, rectal pressure on sense or fullness of balloon) were significantly higher in patients with ultraslow wave than in those without (P<0.001-0.05). The ultraslow wave frequency was inversely proportional to aging and to its amplitude (P=0.006 and <0.001, respectively). Maximal squeeze pressure was closely correlated with maximal resting pressure in a multiple regression analysis (P=0.002). The defecation difficulty and anorectal bleeding were more frequent in patients with ultraslow wave than those without in the hemorrhoids (P=0.008 and 0.021, respectively). CONCLUSIONS: The ultraslow wave closely correlates with an anorectal pressure and frequently occurs in patients with hemorrhoids and chronic anal fissure. It appears to be associated with the internal anal sphincter as well as with the external anal sphincter and levator ani muscles.