ADHD and PTSD are common diagnoses in children with traumatic life events. Because of overlapping symptoms the possibility of misdiagnosis is present. The study encompassed 4881 adolescents 15-16 years of age-50.1 % boys and 49.9 % girls. Youths with and without ADHD symptom scores within the clinical range on the Strength and Difficulties Questionnaire (SDQ) were compared on 12 stressful life events. Approx. 5 % had ADHD symptom scores within the clinical range, and, surprisingly, more girls (6.7 %) than boys (3.4 %). In the ADHD symptom group 58.1 % had experienced two or more stressful life events compared with 26.3 % of those without critical ADHD symptoms and were from 1.6 to 6.6 times more at risk of experiencing such events. Violent life events and parental mental problems were strongest associated with critical ADHD symptoms. Faced with information of negative life events clinicians should evaluate the likelihood of a PTSD diagnosis in adolescents with ADHD symptoms.