Holoprosencephaly is an anomaly in the division of the prosencephalon into cerebral hemispheres during the second month of gestation. Patients can present with early-onset obesity favoured by the cognitive impairment. We present a case of a 24 year-old woman with holoprosencephaly and class III obesity who was treated by 2.4 mg/week SEMAGLUTIDE. Her body weight decreased from 115.3 to 94.3 kg after one-year (18% of total body weight loss). In addition, she presented a marked reduction in self- and hetero-aggressive behaviour when exposed to the sight of food. The treatment was well tolerated, with the exception of a few vomiting when eating palatable food too quickly. GLP1-RAs may be interesting for obesity treatment in the context of neurodevelopmental disorders. They appear to reduce compulsive eating and aggressive behaviour, particularly in relation to exposure to food, and lead to weight loss similar to that seen in people without neurodevelopmental disorders.