To assess the role of anorectal physiologic study for the diagnosis of chronic idiopathic constipation. METHODS: A retrospective study of 81 constipated patients (23 male, 58 female) of mean age 48 16.6 (16~83) years who had no abnormalities in colonoscopy, barium enema, and rectal exam was done. 81 patients underwent defecography and cine-defecography, of which 66 patients underwent anal manometry, 52 patients underwent colonic transit time study (CTT), and 27 patients underwent anal plug electromyography (EMG). RESULTS: Nonrelaxing puborectalis syndrome (NRPR), rectocele, rectal intussusception, anal dyschezia, and sigmoidocele were observed in 27 (33.3%), 26 (32.1%), 14 (17.3%), 3 (3.7%), and 2 (2.5%) of the patients, respectively. Normal cinedefecography finding was observed in 21 (25.9%) patients. More than one abnormal finding was found in 11 (13.6%) patients. Abnormal findings included colonic inertia in 6 (11.5%) patients and pelvic outlet obstruction in 2 (3.8%) patients. Normal colon transit time was observed in 44 (84.6%) patients. Anal hypertonia was observed in 23 (34.8%) patients by anal monometry, of which 3 patients were diagnosed with anal dyschezia in cinedefecography. 13 (48.1%) patients were diagnosed with NRPR in anal plug EMG. The correlation rate between cinedefecography/EMG, defecography/CTT, and CTT/EMG were 81.5%, 61.5%, and 51.9% respectively in the diagnosis of NRPR. Sensitivities of the three tests were 72.7% for cinedefecography, 66.7% for EMG, and 7.7% for CTT in diagnosing NRPR (p<0.05). Positive predictive values of the three tests were 80% for anal plug EMG, 72.7% for cinedefecography, and 50% for CTT in the diagnosis of NRPR. CONCLUSIONS: Defecography and EMG were complements each of the other in diagnosis of pelvic outlet obstruction especially NRPR, but CTT has no role.