A 34-year-old Caucasian woman was diagnosed as having a pigmented iris tumor showing recent growth and satellite lesions. The tumor was associated with pigmentation of the anterior chamber angle and secondary unilateral glaucoma. After local excision, histopathologic studies revealed the plump polyhedral cells typical of melanocytoma. However, the examination of additional sections showed evidence of malignancy. The diagnosis of a melanocytoma that transformed into malignant melanoma was made and later confirmed by electron microscopic studies. Following surgical excision of the tumor, the eye maintained normal intraocular pressure. There was no evidence of recurrence 4 years after surgery.