BACKGROUND: This study investigated the prevalence of DSM-IV Axis 1 mental disorders, deliberate self-harm and suicidal ideation in a sample of Irish adolescents aged 11-13 years. METHODS: A total of 1131 students was surveyed for general psychopathology using the Strengths and Difficulties Questionnaire. Following this, a representative sample of 212 adolescents was assessed for mental disorders, deliberate self-harm and suicidal ideation using the Schedule for Affective Disorders and Schizophrenia for School-Aged Children. RESULTS: 14.6% of the sample met criteria for a borderline score and 6.9% for an abnormal score on the Strengths and Difficulties Questionnaire. Following clinical diagnostic interviews, 27.4% of participants received a current diagnosis of an Axis 1 disorder and 36.8% received a lifetime diagnosis, those rates falling to 15.4% and 31.2% respectively when specific phobias were excluded. CONCLUSIONS: Findings from this study reveal that Irish adolescents aged 11-13 years are experiencing high levels of mental ill-health.