Objective To evaluate the therapeutic effect and safety of letrozole in the treatment of adolescent boys with idiopathic short stature (ISS). Methods A retrospective analysis was performed for the clinical data of 16 adolescent boys with ISS who had a bone age of ≥ 14 years. Among these boys, 8 were initially treated with recombinant human growth hormone (rhGH), followed by rhGH combined with letrozole during a bone age of 14-15.5 years. The other 8 boys were initially treated with rhGH combined with letrozole since their bone age was ≥ 14 years at diagnosis. Of the 16 boys, 16 were treated for not less than 6 months, 12 were treated for not less than 1 year, and 5 were treated for not less than 1.5 years. The increase in bone age, predicted adult height (PAH), final adult height, sex hormones, and adverse reactions after treatment were analyzed. Results After 6 months, 1 year, and 1.5 years of treatment, median bone age was increased by 0 year, 0.5 year, and 0.5 year respectively, which was significantly lower than the increase in age (P < 0.05). There was a significant increase in PAH after treatment (P < 0.05). Seven boys reached final height, which was significantly higher than PAH before treatment (P < 0.05). All the 16 boys had significant increases in luteinizing hormone, follicle-stimulating hormone, and testosterone levels after treatment (P < 0.05), with a significant reduction in the estradiol level and a significant increase in the insulin level at 1 year of treatment (P < 0.05). There was a significant increase in the insulin-like growth factor-1 level at 6 months and 1 year of treatment (P < 0.05). There were no significant changes in blood glucose, blood lipids, uric acid, and the three indices for thyroid function as monitored during treatment (P > 0.05). Conclusions In adolescent boys with ISS and a high bone age, rhGH combined with letrozole can safely and effectively delay the increase in bone age and improve PAH and final adult height, with little adverse effect.