The effect of ad libitum feeding diets with three lysine concentrations to developing gilts housed in groups from 100 to 220 days of age on growth, body composition, feed efficiency and age at puberty was evaluated. Gilts were randomly allotted to three corn-soybean diets formulated to provide three standardized ileal digestible (SID) lysine concentrations. Gilts received grower diets formulated to provide 0.68% (low), 0.79% (medium) or 0.90% (high) SID lysine from 100 days of age until approximately 90 kg BW. Then, gilts were fed finisher diets containing 0.52% (low), 0.60% (medium) or 0.68% (high) SID lysine until they were moved to the breeding barn at approximately 220 days of ageData on BW, bakfat thickness, loin area, feed and lysine intake and age at puberty was collected at different intervals during the study. Gilts fed the low lysine diet had lower average daily gain, body weight, backfat thickness and loin depth compared with gilts fed the high lysine diet. Overall, 34% of gilts displayed standing estrus before 220 days of age. The number of gilts that reached puberty was not different among dietary treatments; however, gilts fed the high and medium lysine diet reached puberty 10 days and 6 days before gilts fed the low lysine diet, respectively. Results from the present study suggest that growth rate can be successfully altered when feeding gilts ad libitum diets differing in SID lysine concentration without negatively affecting puberty attainment.