This investigation was designed to extend our present knowledge of the origin of the anterior spinal a. and is based on 80 brains of human cadavers. The anterior spinal a. is usually formed rostrally by the union of the anterior spinal branches from the intracranial segments of the vertebral aa. In this study, we observed three different locations of the origin of the anterior spinal a. Each type has different characteristics. A bilateral origin (type I) was present in 60 specimens (75%). This type could be further subdivided according to the caliber of the arteries, into the following subtypes: ''balanced'' (type Ia 42.5%), right-dominated (type Ib 17.5%), and left-dominated (type Ic 15%). A unilateral origin (type II) was found in 9 specimens (11.3%), and an origin in an intervertebral transverse anastomosis was demonstrated in 11 (13.8%). In all cases, the anterior spinal a. had an average caliber of 1.145 +/- 0.12 mm.