PURPOSE: Choroidal nevi are generally considered to be stable lesions, and growth of a choroidal nevus is usually believed to be a sign of malignant transformation. We performed this study to determine whether choroidal nevi enlarge over a long period of follow-up without undergoing malignant transformation. DESIGN: Retrospective observational case series. PARTICIPANTS: A total of 278 patients with 284 nevi who had at least 7 years of photographic follow-up without clinical signs of transformation into melanoma were included in the study. METHODS: Data on demographic and clinical information were extracted from patients' charts. Detailed fundus drawings and color fundus photographs were reviewed and compared for evidence of enlargement. MAIN OUTCOME MEASURES: Nevus enlargement without clinical evidence of transformation into melanoma. RESULTS: Of the 278 patients, 69% were female and more than 99% were White with a median age at presentation of 57 years (range, 4-87 years). The largest nevus basal diameter was a median of 5 mm (range, 0.5-14 mm), and the median thickness was 1.5 mm (range, 0.1-3.6 mm). Only 14 nevi (5%) had subretinal fluid outside the nevus, and 6% showed overlying orange pigment. Overlying retinal pigment epithelial alterations included drusen (61%), atrophy (6%), hyperplasia (10%), and fibrous metaplasia (6%). Of 284 nevi, 31% showed slight enlargement over a mean follow-up of 15 years. The median increase in diameter was 1 mm (mean, 0.9 mm; range, 0.2-3.0 mm), and the median rate of enlargement was 0.06 mm/yr (mean, 0.06 mm/yr; range, 0.01-0.36 mm/yr). None of the lesions that enlarged developed new risk factors that are generally associated with malignant transformation. Frequency of enlargement was 54% in patients aged less than 40 years and 19% in patients aged more than 60 years. On multivariate analysis, younger patient age was the only factor predictive of nevus enlargement (P<0.001). CONCLUSIONS: With long-term follow up, 31% of choroidal nevi showed slight enlargement without clinical evidence of transformation into melanoma. The frequency of enlargement was inversely related to patient age.