A case of unilateral iris cyst in an infant aged three months is reported. The cyst was excised and subjected to light and electron microscopy, the results of which verified the analogy of the cystic wall with the conjunctival epithelium, which likewise was examined. Further, proliferations of pigment epithelium were found along the pupillary border. Most likely some of the iris cysts are due to aberrant conjunctival epithelium, which possibly had invaded the chamber i n connection with the formation of the lens vesicle.