The experience in 54 intracranial arterial aneurysms operated on with microsurgical technique during the period of January 1971 to March 1974 is reported. In 40 patients classified in Groups I, II and III, there were no mortalities. Including 8 patients of Group IV with 3 deaths, the mortality rate was 6.2%. In the patients from Group V, the mortality rate continues to be prohibitive, regardless of the technique used. The patients were operated on with the surgical microscope made in Brasil, using clips of Yasargil, Scoville, Mayfield and some of the author's model. Comparing the present microsurgical results from 1971 to 1974 with the previous experience based on nearly 400 cases from the period of 1949 to 1970, the author concludes that the surgery of aneurysms with the help of the microscope is simple and without mortality in the patients of good surgical risk. He considers the existence of spasm as the greatest problem and judges that the best moment to operate is when clinical improvements appear, coinciding with the disappearance of the spasm, generally between the 7th and 10th days.