Several studies have investigated the variations in the anatomy of each segment of circle of Willis whereas a few have addressed the variations of this arterial circle as a whole. In this study the entire circle of Willis and its variations were studied in a cohort of Iranian people and compared with previous reports. Methods: Anatomical variations of the circle of Willis in 132 brains of Iranian cadavers (102 male adults and 30 fetuses and infants) were studied. The dissection process was digitally filmed for further studies. Using computer software the external diameters of the vessels were measured and the circle variations were classified. The variations of the circle as a whole and segmental variations were compared with previous studies. Results: Uni-and bilateral hypoplasia of posterior communicating arteries (PcoAs) constituted the most common variation in our study which was similar to previous works. Aplasia of the anterior cerebral artery (A1) and the posterior cerebral artery (P1) were not observed. In 3.3% of fetuses and infants and 3% of adult instances both right and left posterior communicating arteries were absent. There was one case of anterior communicating artery (AcoA) aplasia in adult group. Conclusions: The anatomical variations discovered in Iranian circle of Willis in this study were not significantly different to those of more diverse populations reported in the literature. The main differences between the fetal and adult disposition are the diameter of the PcoA and the circular part of the P1.