The purpose of this study was to characterize the clinical course of myopia in a selected pediatric population. The computerized records of a health maintenance organization provided longitudinal data on 501 children aged 5 to 15 years. We examined the influence of age at diagnosis, gender, race, and initial refraction on progression of myopia. Mean follow-up was 34 months, with 75% of children having follow-up longer than 16 months. The mean rate of myopic progression was greater for children whose myopia was diagnosed at a younger age (5-7 years, -0.56 diopters/year versus 11-15 years, -0.28 diopters/year; p < 0.0001). Children with more than one diopter of myopia at first diagnosis progressed faster than children with less than or equal to one diopter of myopia (mean rate -0.48 diopter/year versus -0.41 diopter/year; p = 0.05). Cumulative event rate curves suggest a gender effect in the prepuberty years of 8 to 10, with myopia progressing faster in girls than boys (p = 0.003). Progression of myopia did not differ between white and non-white children. More rapidly progression of myopia is associated with younger age at initial diagnosis and greater severity of initial myopic refraction.