A 1-month-old white girl developed a rapidly progressing congenital nonpigmented iris cyst covering the pupil and displacing the lens and ciliary body. The cyst was completely removed using a modified block excision (9 x 3.5 mm). The tumor consisted of partially keratinizing cuboidal epithelium with goblet cells, which was covered by proliferating corneal endothelium on the outside. Histopathological, and scanning and transmission electron microscopic findings are described. The postoperative course is unremarkable for 1 year. To our knowledge this case is the first case of a congenital iris cyst successfully treated with block-excision.