The author reports 52 interhemispheric and percallosal operations carried out by himself and certain of his associated trainees upon 50 patients presenting 19 different pathological entities over a period of 38 years (1944 through 1982). The still too little appreciated advantages of this approach over transcortical avenues to the anterior ventricular system are described, together with specific indications, contraindications, and reliable and proven surgical techniques. The long term results are examined for four different outcomes: (a) recovery without deficit or with a deficit wholly chargeable to the lesion before its extirpation; (b) recovery, but with a deficit produced by or increased by the surgical procedure; (c) failure to benefit; and (d) death due to the operation. Eleven patients had invasive tumors that were not totally removable, and 6 died postoperatively. Five survived with disease-produced deficits that failed to disappear. Two had permanent deficits due to intraoperative misfortunes. Twenty-six made full recoveries, with return to work or school. Only 1 patient had a postoperative seizure problem.