Background/Objective: The Strengths and Difficulties Questionnaire self-report (SDQ-S) has been extensively used to assess mental health problems among children and adolescents. However, previous research has identified substantial age and country variation on its psychometric properties. The aim of this study was three-fold: i) to evaluate internal structure and measurement invariance of the Spanish version of the SDQ; ii) to analyze age and gender-specific effects on the SDQ subscales; and iii) to provide Spanish normative data for the entire age range of adolescence. Method: Data were derived from two representative samples of adolescents aged 14 to 19 years old, selected by stratified random cluster sampling years (N = 3378). Results: The reliability of the Total difficulties score was satisfactory, but some subscales showed lower levels of internal consistency. Confirmatory factor analysis supported the original five-factor model. Finally, results revealed that SDQ scores were influenced by the gender and the age of participants; thus, the normative banding scores and cut-off values were provided accordingly. Conclusions: This study validates the Spanish SDQ-S for the entire age range of adolescence. However, more cross-country and cross-age research is needed to better understand the inconsistent findings on SDQ reliability.