The appearance of the anterior chamber angle shows considerable variation in eyes with glaucoma caused by congenital or developmental causes. These differences, in over 100 eyes studied, correlate well with the effectiveness of trabeculotomy in controlling the intraocular pressure. In angles harboring what is probably embryonic mesoderm (although they may vary in their gonioscopic appearance), prognosis for control of IOP by trabeculotomy is excellent, while in those that show evidence of a fibrotic process at the limbus, the prognosis for trabeculotomy is hopeless. The latter, once recognized, should be treated by trabeculectomy, this condition being the only good indication for trabeculectomy in these eyes.