Fourteen patients (ten women, four men) with iris nevus (Cogan-Reese) syndrome, all having unilateral glaucoma, were studied clinically. Many had corneal edema, and all had changes in the iris consisting of one or more of the following: iris whorls or nodules or both, atrophy of iris stroma, heterochromia (the darker iris usually involved), or ectropion uveae. All had peripheral anterior synechias. Material for histological study was available from ten patients and showed a nonmalignant diffuse nevus of the anterior surface of the iris. An overgrowth of endothelium and Descemet membrane extending onto the iris surface may be a characteristic part of the process. Patients tended to be women in middle age. Conservative treatment avoiding enucleation is advised. Whenever a patient with suspected iris nevus syndrome or essential iris atrophy is subjected to glaucoma surgery, a biopsy specimen of the iris should be obtained for histological study.