This paper has presented the author's experience with the evaluation and follow-up of 62 patients with primary cysts of the iris. On the basis of these observations, a classification of iris cyst is proposed. Accordingly, primary iris cysts are divided into epithelial and stromal categories, each having different clinical characteristics. Epithelial cysts arise between the pigmented epithelial layers of the iris and occur at the pupillary margin (central cysts), in the mid-portion of the iris (midzonal cysts) or, more commonly, in the iridociliary sulcus (peripheral cysts). In some cases, the cysts apparently break free from their epithelial attachment and migrate into the anterior chamber of vitreous chamber (dislodged cysts). Primary stromal cysts occur within the iris stroma and are not directly continuous with the posterior epithelium. They apparently arise from ectopic surface epithelium which is trapped in the iris during embryologic development. A study of the natural course and complications of these lesions has shown that the great majority of primary iris cysts, particularly those which arise from the iris pigment epithelial layer, are stationary lesions which rarely progress or cause visual complications. This finding is contradictory to the contemporary belief of certain authorities who stress that many such lesions lead to severe complications with blindness and loss of the eye. The natural course of primary epithelial cysts differs from that of secondary iris cysts which follow surgical or non-surgical trauma. The latter lesions do frequently enlarge and lead to severe complications such as inflammation and glaucoma.