Assessment of sexual maturation in adolescence is crucially important in clinical practice, because the possibility of concealed disease during the earlier period of child development needs to be detected. However, to undress children sometimes is problematic and unethical in several countries. Therefore, in this study the authors evaluated the concordance between children's self-assessment by Tanner photograph with a written description, and examination by pediatricians. One hundred and ninety four children (100 girls, 94 boys), aged 7-15 years, were recruited in this study. The outcome demonstrated that the two processes of investigation were in good concord: the weight kappa of 0.76 and 0.79 for the breast stage (B) and pubic hair stage (PH), respectively, in girls. In boys, the weight kappa were 0.59 and 0.73 for genital stage (G) and pubic hair (PH) stage, respectively. However, the weight kappa for genital stage was improved after the subjects were provided more time to examine themselves before choosing the photograph. In girls, the mean chronological age (CA) for B stage II, III, IV was 10.4+/-1.3, 12.5+/-1.3, 13.6+/-0.7 years and for PH stage II, III, IV was 11.9+/-1.4, 12.9+/-1.2, 13.5+/-0.9 years. The normal CA for the onset of puberty in girls was between 7.8-13.0 years. In boys, the mean CA for G stage II, III, IV was 11.3+/-1.7, 12.4+/-1.2, 13.2+/-1.2 years, and for PH II, III, IV was 12.2+/-1.3, 13.1+/-1.0, 13.9+/-1.7 years. The normal CA for the onset of puberty in boys was 7.9-14.7 years. In addition, the authors constructed the normal value for penile length in Thai boys, aged between 9-15 years, to be used as a reference. Therefore, this study demonstrated a good concordance between the self-assessment by Tanner photograph and examination by pediatricians. This can be applied for use in filed research, school screening and clinical practice.