PURPOSE. The present study investigated the relationship between parental refractive error and myopia progression in their offspring and the interaction between parental ametropia and the effects of wearing progressive-addition (PALs) or single-vision (SVLs) lenses on the progression of myopia in children enrolled in the Correction of Myopia Evaluation Trial (COMET). METHODS. The progression of myopia in a subset of COMET children (N = 232; 49% of initial group) was defined as the difference in mean spherical equivalent refraction of both eyes obtained by cycloplegic autorefraction between the baseline and 5-year visit. Parental refractions were obtained by noncycloplegic autorefraction (81%) or from recent eye examination records (19%). RESULTS. The number of myopic parents (mean spherical equivalent refraction ≤-0.75 D) was directly related to myopia progression among children wearing SVLs: myopia in children with no (zero) myopic parents progressed (mean ± SE) -1.81 ± 0.18 D and with one myopic parent, -2.04 ± 0.13) D; these amounts were significantly less than the progression of children with two myopic parents (-2.59 ± 0.19 D). In the PAL group, progression was not significantly related to the number of myopic parents and was -2.01 D overall. Among children with two myopic parents, progression was -2.00 D in the PAL group, significantly less than the progression of children wearing SVLs (P = 0.03). Among children with zero or one myopic parent, progression did not differ significantly between the lens groups. When the data were adjusted for covariates, the interaction between treatment effect and number of myopic parents was significant (P = 0.01). Over the 5-year study period, axial length increased 0.93 ± 0.07 mm in children with two myopic parents wearing PALs and 1.18 ± 0.07 mm in children with two myopic parents wearing SVLs (P = 0.01). The axial length increase in children wearing SVLs and with two myopic parents was significantly more than the 0.89 ± 0.07 mm increase in children wearing SVLs and with zero myopic parents (P = 0.015). CONCLUSIONS. Parental refraction was related to myopia progression and changes in axial length. Among COMET children with two myopic parents, myopia progression and increases in axial length were slower in the group wearing PALs than in those wearing SVLs, by a statistically significant but clinically minor amount. Because this study was ancillary to COMET and the present analyses are based on a subset of participants, conclusions must be regarded as suggestive. Copyright © Association for Research in Vision and Ophthalmology.