It is suggested that patients with defecation disorders (DD) strain excessively or do a Valsalva maneuver (VM) during evacuation, resulting in rectoanal discoordination, which hinders rectal evacuation. However, definitive data are lacking. Rectoanal pressures during evacuation and a VM were measured with seated high-resolution manometry (HRM) in 64 healthy and 136 constipated women with a normal (84 women, C-normal) or prolonged (52 women, C-abnormal) balloon expulsion time (BET). The number of abnormal rectoanal parameters during evacuation and the joint distribution of pressures during evacuation and a VM were used to discriminate between controls and C-abnormal BET patients. The peak anal pressure (5 s) during a VM accounted for 0%, 26%, and 49% of the variance in anal pressure during evacuation in healthy women, C-normal BET, and C-abnormal BET. The association between anal pressure during a VM and evacuation was stronger in C-abnormal BET than in healthy women and C-normal BET (p for interaction <0.001). Fifty-eight of 64 controls and 33 of 52 C-abnormal BET patients had no or one abnormal parameter during evacuation; hence, the probability of C-abnormal BET was 33/91 (36%). In patients with no or one abnormal parameter during evacuation, a logistic model based on anal pressures during evacuation and a VM discriminated between controls and patients with C-abnormal BET with a sensitivity and a specificity of 67% and 75%. Assessment of rectoanal pressures during evacuation and a VM uncovers rectaoanal discoordination and facilitates the diagnosis of DD in selected patients.