The results of a prospective survey of the ophthalmic manifestations of neurofibromatosis (NFT) have never been published. We studied the ocular features of NFT in 77 patients (ages 5 weeks to 69 years) among whom the diagnosis was made by nonophthalmic parameters. Of subjects ages 6 years and older, 92% had hamartomatous lesions of the iris, termed Lisch nodules, as distinguished from common iris nevi in nonaffected individuals. The presence of Lisch nodules is correlated to age, but not to number of café-au-lait spots, number of neurofibromata, or severity of disease. Lisch nodules appear among prepubertal children and are apparently unique to NFT. They are a valuable criterion by which to diagnose NFT in problematic cases.