Purpose: Defecatory disorders are diagnosed by rectal balloon expulsion (BE) and anorectal manometry, which are traditionally evaluated in the seated and left lateral (LL) positions respectively. This may explain the observed limited correlation between rectoanal gradient (manometry) and balloon expulsion. Hence, our aims were to compare manometry with BE in the LL and seated positions. Methods: Sixty-two healthy women and 158 women with Rome II criteria for chronic constipation were included in the study. Balloon expulsion was assessed in seated (time needed to expel the balloon: normal - ≤60 s, abnormal - >60 s) and left lateral (additional traction weight needed to expel the balloon: normal - ≤100 g, abnormal - >100 g) positions. Based on BE, patients were classified into four groups: normal in both positions, abnormal in left lateral position only, abnormal in seated position only and abnormal in both positions. Anorectal pressures (rest, squeeze, and simulated evacuation (SE)) were measured by high resolution manometry (HRM). Demographic, manometry and clinical data was compared using chi-square and t-tests. Multivariable logistic regression was used to assess predictors of balloon expulsion in both positions. Results: BE performed in seated and left lateral positions was concordant in 173 subjects (normal in both positions - 141, abnormal in both positions - 32), and discordant in 47 subjects (abnormal only in left lateral position - 30, abnormal only in seated position - 17). There was modest agreement (κ=0.43 [95% CI 0.30-0.57]) between seated and left lateral BE. Age, BMI, anal resting and squeeze pressure, length of anal sphincter and squeeze duration were not significantly different among groups (Table). However, compared to subjects with normal BE in both positions, anal relaxation during simulated evacuation (SE) was lower, anal pressure during SE was higher, and the rectoanal gradient during SE was more negative in the 3 other categories; these variables were all associated (p ≤ 0.0004) with group status. High anal pressure during SE (OR1.02, 95% CI 1.00-1.04) and high rectal sensory threshold for desire to defecate (OR1.01, 95% CI 1.00-1.02) were associated with increased risk of abnormal BE in both positions, whereas high rectal pressure during SE (OR 0.96, 95% CI 0.93 - 0.98) was associated with lower risk.Table: [1720] Comparison of Symptoms and Anorectal Parameters among GroupsConclusion: This case-control study demonstrates modest agreement between rectal balloon expulsion in the left lateral and seated positions. In addition to abnormal seated BE, which is considered indicative of pelvic floor dysfunction, HRM findings suggest that even some patients with abnormal BE in the left lateral position have pelvic floor dysfunction.