Background/Aims: Chronic constipation is a common gastrointestinal disorder diagnosed using Rome III criteria. Defecography is a radiographic method used to identify anatomic abnormalities of anorectum. The present study aimed to evaluate the defecographic findings in patients with severe idiopathic chronic constipation. Methods: One hundred patients, who complained of severe idiopathic chronic constipation with abnormal balloon expulsion test, underwent defecography after injection of barium. An analysis of radiographs was performed by an expert radiologist for the diagnosis of descending perineum syndrome, rectocele, enterocele, rectal ulcer, rectal prolapse, fecal residue of post defecation, and etc. Then, they were compared between the two sexes. Results: Normal defecography was only observed in two participants. Descending perineum syndrome was the most common abnormality (73.3%). The results showed that rectocele (80.8%) and descending perineum syndrome (69.2%) were most frequent in women. In males, descending perineum syndrome and rectal prolapse were more prevalent (87% and 43.5%, respectively). Compared with men, rectocele and rectal ulcer were more frequently observed in women (p<0.001, and p=0.04, respectively), while men were more affected by descending perineum syndrome (p=0.04). In total, women had a greater incidence of abnormal defecographic findings compared with men (p=0.02). Conclusions: Defecography can be performed to detect anatomic abnormalities in patients with severe idiopathic chronic constipation and abnormal balloon expulsion test. This technique can assist physicians in making the most suitable decision for surgical procedure. (Korean J Gastroenterol 2017;70:39-43)