Objective The objective of this study was to evaluate the effects of sexual maturation on anthropometric parameters and basic physical characteristics in male adolescents aged from ten to fourteen years old. Materials and Methods The biological age was studied through the evaluation of the stage of the external genitalia development. Other evaluated characteristics were: total body mass (MCT), stature, body mass index (BMI), bone age (IO), strength, speed, agility and aerobic power. Results The results showed significant differences in all variables related to growth (chronological age, height, total body mass, body mass index and bone age) between different stages of sexual maturation. In relation to physical qualities, among maturational stages, we find significant differences in most characteristics, except for agility. Conclusions Based on this study, we may conclude that sexual maturation, evaluated by the stages of development of the external genitalia, exerts great influence on the anthropometric variables, the bone age and the basic physical characteristics of adolescent boys.