The work is based on the compilation of European data about skeletal and sexual maturation and on the long-term clinical experiences and primary exact results. It represents the basis for biological age assessment in routine pediatric practice. Due to the high correlations of sexual and skeletal maturity the author recommends the orchidometry as a necessary pediatric method in biological age assessment in boys. An analogy characteristic of biological age in girls is represented by the mammary gland development and its classification according to Marshall and Tanner. The testicular volume and breast development are the significant correlates of hormonal situation, which limits skeletal and sexual maturation of organism in boys and girls, respectively. Skeletal maturity in healthy individuals exactly matches sexual maturity. The exact evaluation of auxological parameters of sexual maturity combined with growth velocity analysis offers the rapid, inexpensive, non-invasive and exact way for biological age assessment, which is necessary for the good quality of growth diagnostics in pediatrics.

        Key words: biological age assessment, skeletal maturity, bone age, sexual maturity, testicular volume, breast development