The anatomy of the Anterior Communicating Artery complex is studied with the aid of the Zeiss operating microscope in 75 human brains removed at autopsy. The variations in the structure of the Anterior Communicating Artery and the A1 and A2 segments of the Anterior Cerebral Artery are reported. Special attention is given to the site of origin and number of branches from the Anterior Communicating Artery and the site of origin of Heubner's arteries. The necessity of using the operating microscope during surgical treatment of aneurysms of the Anterior Communicating Artery complex is stressed.