The aims of this study were (1) to establish an objective baseline to assess the severity of rectoanal intussusception by the depth of rectal infolding and (2) to compare manometric and defecographic parameters in patients to validate this new objective classification of intussusception. Between July 1988 and September 1997, 224 patients with rectoanal intussusception confirmed by cinedefecography who underwent anal manometry were evaluated. These patients were classified into two groups based on the depth infolding: group I (n = 163), intussusception < 10 mm infolding seen on the rectal wall; and group II (n = 61), intussusception ≥ 10 mm infolding extending into the anal canal. There were 32 males and 192 females, of a mean age of 61 years (range, 19-88). Patients were subdivided into 5 groups according to their dominant complaint. Complaints were constipation with incomplete evacuation (n = 113, 69.3%), fecal incontinence (n = 28, 17.2%), rectal pain (n = 19, 11.7%) and others (n = 3, 1.8%) in group I, and constipation (n = 34, 55.7%), sensation of prolapse (n = 14, 23.0%) and others (n = 13, 21.3%) in group II. There was a significant difference in the degree of intussusception relative to sensation of prolapse (p < 0.05). Manometry showed that the rectoanal inhibitory reflex was absent more often in patients in group II (19.7% vs. 8.5%) than in group I (p < 0.05). Moreover, group I patients had higher mean and maximum squeeze pressures when compared to group II (78.1 vs. 62.5, 105.9 vs. 88.8 mm Hg, respectively, p < 0.05). The incidences of combined cinedefecographic anomalies, such as rectocele, sigmoidocele and perineal descent, were high: 85.2% in group II and 79.1% in group I (p > 0.05). In conclusion, this study showed manometric and symptomatic differences relative to the size of the intussusception. The decreased pressure seen in patients with larger intussusception may auger for the subsequent development of incontinence in these patients.