This neuroanatomic study has been performed to establish the frequency of potenciais anastomosis in the posterior portion of the cerebral arterial circle in 87 brains from northeasterner brazilians without any aparent clinical manifestations of neural dysfunction. The fetal pattern of the posterior communicating branch was present in the 46% (40/87) of the cases. The frequency with regard to side was the following: 21,8% (19/87) on the right side; 13,8% (12/87) on the left side and 10,4% (9/87) bilateral. The bilateral and unilateral potenciais anastomosis at level of the posterior communicating branches, with fetal pattern or with gross caliber (Padget, 19483), were present in the 71,2% (62/87) of the arterial circles. The bilateral potenciais anastomosis were formed by two posterior communicating branches with fetal pattern in the 10,4% (9/87) of the cases, by two of those vessels of gross caliber in the 11,5% (10/8/) of the circles, and by one fetal posterior communicating branch, and one contralateral posterior communicating branch of gross caliber in the 13,8% (12/87) of the cases. Unilateral potenciais anastomosis constituted by fetal posterior communicating branch (21,8%) or by posterior communicating branch with gross caliber (13,8%) ocurred in the 35,6% (31/87) of the arterial circles.