AIM: Children with autism spectrum disorders (ASD) often present with emotional and behavioral problems, which could change the clinical course, especially during childhood, and affect future quality of life. The aim of this study was to clarify the age- and sex-related differences of these problems in ASD. METHODS: The study subjects were 173 patients with ASD (age: 4-16 years) and 173 age- and sex-matched community children (control group). The parent version of the Strengths and Difficulties Questionnaire was used for comparison of the emotional and behavioral problems between the two groups. RESULTS: The Strengths and Difficulties Questionnaire scores were significantly higher in children with ASD than controls at all ages. The score of total difficulties was significantly higher in girls with ASD than in boys, while the score in male controls was significantly higher than in female controls. Age-related differences in emotional and behavioral problems were observed both in children with ASD and controls, but the characteristics were different: in children with ASD, emotional symptoms and peer problems in both sexes and conduct problems in girls increased significantly with age, while none of the problems in the controls changed with age except for a decrease in the score of hyperactivity/inattention developmentally in both sexes. Prosocial behaviors of children with ASD and controls showed small changes with age. CONCLUSION: Emotional and behavioral problems are common in children with ASD and showed age- and sex-related differences. Our study emphasizes the importance of recognizing those differences among children with ASD for early intervention.