Several reports of coccygodynia have been confined to the causes, the methods of treatment, and the methods of radiological examination. As far as we know, there has been no previous study about the objective measurement of the coccyx. The purpose of this study was to find the possible cause of idiopathic coccygodynia by comparing the clinical and radiological differences between traumatic and idiopathic coccygodynia by innovative objective clinical and radiological measurements. Thirty-two patients with coccygodynia were evaluated retrospectively. We divided the patients into two groups. Group 1 consisted of 19 patients with traumatic coccygodynia and group 2 consisted of 13 patients with idiopathic coccygodynia. We reviewed medical records and checked age, sex distribution, symptoms, and treatment outcome in each group. We also reviewed coccyx AP and lateral views of plain radiological film and measured the number of coccyx segments and the intercoccygeal angle in each group. The intercoccygeal angle devised by the authors was defined as the angle between the first and last segment of the coccyx. We also checked the intercoccygeal angle in a normal control group, which consisted of 18 women and 2 men, to observe the reference value of the intercoccygeal angle. The outcome of treatment was assessed by a visual analogue scale based on the pain score. Statistical analysis was done with Mann-Whitney U test and Chi-square test. Group 1 consisted of 1 male and 18 female patients, while group 2 consisted of 2 male and 11 female patients. There were no statistically significant differences between the traumatic and idiopathic coccygodynia groups in terms of age (38.7 years versus 36.5 years), male/female sex ratio (1/18 versus 2/11), and the number of coccyx segments (2.9 versus 2.7). There were significant differences between the traumatic and idiopathic coccygodynia groups in terms of the pain score (pain on sitting: 82 versus 47, pain on defecation: 39 versus 87), the intercoccygeal angle (47.9 degree versus 72.2 degrees), and the satisfactory outcome of conservative treatment (47.4% versus 92.3%). The reference value of the intercoccygeal angle in the normal control group was 52.3 degrees, which was significantly different from that of the idiopathic group. In conclusion, the intercoccygeal angle of the idiopathic coccygodynia group was greater than that of the traumatic group and normal control group. Based on the results of this study, the increased intercoccygeal angle can be considered a possible cause of idiopathic coccygodynia. The intercoccygeal angle was a useful radiological measurement to evaluate the forward angulation deformity of the coccyx.