Objectives: Defecation proctography (DP) is the standard method used in the investigation of obstructed defecation, a common cause of constipation. Translabial ultrasound has been shown to demonstrate rectocele, enterocele, rectal intussusception and levator activation. In order to define advantages and disadvantages of ultrasound and DP, and to determine agreement, we performed a comparative clinical study. Methods: Thirty-seven women booked for DP for obstructed defecation were recruited. Multiple fluoroscopic images were acquired using a Philips MD3 digital C-arm X-ray system. Translabial ultrasound was performed using a GE Kretz Voluson 730 expert system, after voiding, supine, at rest and on maximal Valsalva. All patients rated discomfort on a scale of 0–10. Using both methods, we determined the anorectal angle at rest and Valsalva, presence of a rectocele and its depth, as well as presence of rectal intussusception or prolapse. Measurements were undertaken by different operators who were blinded to other data. Results: Mean age was 53 (26–80) years. Six women did not attend the DP, leaving 31 cases for comparison. Patients rated the discomfort of ultrasound at 1.58/10 (SD 1.57), whereas the DP was rated at 5.71 (SD 3.52) (P < 0.001). On comparing the methods, Cohen’s kappa was 0.26 for rectocele, and 0.09 for rectal intussusception/prolapse. Measurements of anorectal angle and rectocele depth did not correlate significantly. Positive agreement between methods was 82% for rectocele and 88% for intussusception, but negative agreements were 43% and 28% only. Conclusions: Ultrasound of the anorectum is capable of diagnosing rectocele and rectal intussusception. There is no radiation exposure; ultrasound is better tolerated and also yields information on the lower urinary tract, prolapse and the levator ani. While correlations between ultrasound and DP were generally poor, there was high positive agreement for rectocele and intussusception, suggesting that DP could be avoided in patients in whom these diagnoses are made by ultrasound.