Seven cases of parietal cephalocele and three cases of occipital cephalocele associated with abnormal venous drainage were evaluated, and the mechanism of the development for venous system was discussed from the embryological viewpoint. In parietal cephaloceles the abnormally draining vein, which corresponds to the straight sinus, ascended along the interhemisphere apart from the tentorium and emptied into the superior sagittal sinus below the cephalocele. The superior sagittal sinus formed the confluence, which was positioned high up. Intraoperative findings revealed that cephalocele penetrated the superior sagittal sinus at the midline. In the case of occipital cephalocele, the straight sinus followed a postero-superior course, to drain into the confluence just above the neck of cephalocele. The results of our study suggest that the causation of abnormal venous drainage in the great vein of Galen, the straight sinus and the superior sagittal sinus may be secondary, through interaction with a developmentally pre-existing cephalocele.