Although childhood trauma and family adversity can increase vulnerability to serious mental health problems, uncertainty exists about the nature and prevalence in a clinical population. This embedded research aims to establish the prevalence of trauma and adversity in young people seeking help from Child and Adolescent Mental Health Services (CAMHS). All children, adolescents, and their parents/guardian attending their initial assessment at a CAMHS service were invited to participate in the ‘Stressful Life and Family Difficulties study’ and a clinical interview. 162 families participated in the study. It was more common for young people to experience multiple adversities (three or more) in the last 12 months than single events. Mothers self-reported a greater number of family adversities than fathers. According to clinicians, the most frequent adversities experienced by young people were having a parent with a mental illness (66%), being bullied (63%) and parental divorce or separation (43%). Overall, clinicians reported that 69% of CAMHS clients had experienced a potentially traumatic experience (any physical, emotional or sexual abuse, child neglect or traumatic event). Moreover, young people with trauma histories were significantly more likely to have a parent with a history of trauma.