Objectives: To compare the humeral retrotorsion (HRT) among non-athletes, amateur swimmers and competitive swimmers and to analyze the relationship between HRT and swim volume in competitive swimmers. Design: Cross-sectional. Setting: Laboratory. Participants: Ninety children and adolescents, both genders (30 non-athletes: 11.50 ± 1.94 years; 30 amateur swimmers: 11.56 ± 1.81 years; and 30 competitive swimmers: 12.63 ± 2.02 years). Main outcome measures: HRT measurement through the bicipital forearm angle (BFA), by palpation, using an inclinometer to obtain the angle. Results: Competitive swimmers showed lower BFA (higher HRT) compared to the amateurs (mean difference: 8.3°; p = 0.013; effect size: 0.82) and to the non-athletes (mean difference: 8.5°; p = 0.010; effect size: 0.80). A significant fair negative relationship (r = −0.37; p = 0.04) was found between BFA and volume of swim. Conclusion: Competitive young swimmers present increased HRT and a higher volume of swim is associated with a lower BFA (higher HRT) in these athletes. These results can help to improve the understanding of osseous adaptations in young swimmers.