BackgroundObesity is a growing global health concern, and those with a developmental disorder are at particular risk. Elevated levels of childhood trauma, placement breakdowns and obesity have been documented in the developmental disorder population, yet their relative associations remain unclear. ObjectiveA previous study (Morris et al., 2020) highlighted a high prevalence of adverse childhood experiences (ACEs) and obesity in adolescents with developmental disorders residing in a secure inpatient setting. The current cross-sectional study sought to further explore the prevalence of placement breakdowns and its relationship with Body Mass Index (BMI) in this sample. MethodsSecondary analysis was conducted on existing data for 34 adolescents, aged 10–17 years at admission, held in a secure mental health hospital developmental disorder service in the United Kingdom (UK) under the Mental Health Act. ResultsAlmost half of participants had experienced a placement breakdown (47.1%), the majority of whom typically experienced multiple breakdowns (M = 3.94, SD = 2.14). Placement breakdowns significantly predicted BMI and had a predictive effect that was independent to and above that of ACEs. ConclusionsPlacement breakdowns significantly contribute to risk for obesity, above that explained by early adversity. Those who have experienced placement breakdowns have a greater risk for obesity, irrespective of their level of exposure to ACEs. A history of previous placement breakdowns may act as a red flag for obesity.