Purpose: to investigate the effects of vessel geometry on steno-occlusive and dilatative common iliac artery (CIA) pathologies. Methods: this single-center, retrospective study included 100 participants, namely 60 participants with a unilateral, isolated CIA pathology who were divided into three pathology-based groups (a stenosis group, n = 20, an occlusion group, n = 20, and an aneurysm group, n = 20) and 40 participants without a CIA pathology (control group). All participants underwent abdominal and pelvic computed tomography angiography. The aortoiliac region of the participants was reconstructed into three-dimensional models. Elongation parameters (tortuosity index (TI) and absolute average curvature (AAC)) and bifurcation parameters (iliac take-off angle, iliac planarity angle, and bifurcation angle) were determined using an in-house-written piece of software. Demographic data, anthropometric data, cardiovascular risk factor data, and medical history data were obtained from participants’ electronic health records. The following statistical methods were used: one-way ANOVA, chi-square test, t-tests, Wilcoxon test, Kruskal–Wallis test, and multivariate linear regression. Results: in the occlusion group, both TI and AAC values were significantly higher on the contralateral side than on the ipsilateral side (both p < 0.001), whereas in the aneurysm group the AAC values were significantly higher on the ipsilateral side than on the contralateral side (p = 0.001). The ipsilateral and contralateral TI and AAC values of the iliac arteries were significantly higher in the aneurysm group than in the other three groups (all p < 0.001). Age significantly affected all of the elongation parameters except for the TI of the infrarenal aorta (all p < 0.010 except the TI of the infrarenal aorta). In addition, the AAC values for the iliac arteries were significantly associated with obesity (ipsilateral iliac artery, p = 0.045; contralateral iliac artery, p = 0.047). Aortic bifurcation parameters did not differ significantly either within each group (ipsilateral versus contralateral side) or between the individual groups. Conclusions: occlusions tend to develop in relatively straight iliac arteries, whereas unilateral, isolated CIA aneurysms are more likely to occur in elongated aortoiliac systems.