Purpose: To evaluate topographic corneal changes in relatives of patients with keratoconus (KCN). Methods: In a prospective Study, 300 eyes of 150 relatives of 45 patients with KCN were evaluated. Complete slit-lamp examination, refraction, and corneal topography were performed for all eyes. The topographic indices for diagnosis of KCN were from Rabinowitzcriteria. Results: The Study included 84 (56%) female and 66 (44%) male subjects. Mean age was 32.4 +/- 15 years (range, 16-83 years'). KCN was diagnosed in 14% of the subjects and another 7.3% were suspicious for KCN. The overall prevalence of astigmatism was 58%, including 42.1% in the KCN group, 66.7% in the KCN suspect group, and 49.6% in the healthy group. Thirty-one eyes had high regular astigmatism (>1.5 D) including 17 (54.8%) in the KCN group and 14 (45.2%) in the healthy group. Oblique astigmatism was seen in 33 (11%) eyes, including 34.2% in the KCN group, 47.6% in the suspicious KCN group, and 4.6% in the healthy group. Conclusions: Relatives of patients with KCN have a high prevalence Of Undiagnosed KCN. Corneal topography is important for the diagnosis of KCN and KCN Suspects in family members of patients with KCN. Therefore. keratorefractive Surgery should be considered cautiously in these individuals.