Objective: Differences between adolescent self-reported and parent-reported emotional and behavioural difficulties may influence psychiatric epidemiological research. This study examined concordance between adolescents and their parents about mental health symptoms using the Strengths and Difficulties Questionnaire. Methods: The study comprised a randomly selected, nationally representative sample of adolescents aged 11–17 years who participated in the Second Australian Child and Adolescent Survey of Mental Health and Wellbeing (N = 2967). Matched adolescent and parent responses across the five Strengths and Difficulties Questionnaire subscales (emotional problems, hyperactivity, peer problems, conduct problems and prosocial behaviour), as well as total difficulties and total impact scores were examined to estimate concordance. Concordance patterns were analysed by sex, after stratifying the sample by age group (younger adolescents: 11–14 years; older adolescents: 15–17 years). Results: Concordance was 86.7% for total difficulties, 77.5% for total impact and ranged from 82.4% to 94.3% across the five Strengths and Difficulties Questionnaire subscales. There were no differences in concordance between sexes on the total difficulties score. Older females were more likely to disagree with their parents about emotional problems compared to males of the same age. Younger males were more likely to disagree with their parents compared to same-aged females about peer problems, hyperactivity, conduct problems and prosocial skills, as well as the impact of their problems. Older males were more likely to disagree with their parents about their prosocial skills compared to older females. Conclusion: Overall, concordance between adolescents and parents on the Strengths and Difficulties Questionnaire was largely driven by the high proportion of respondents who reported having no problems. Discordance on a subscale increased as the prevalence of problems in a sex and age demographic subgroup increased. These findings highlight the need for a multi-informant approach to detect emotional and behavioural difficulties in adolescents, particularly when assessing the impact of symptoms, as this subscale had the lowest concordance.