Severe obesity is a common consequence of hypothalamic region diseases and their treatment. Only two previous case reports have described hypothalamic lipomas in children with obesity. We described a case of an adult with severe obesity associated with hypothalamic lipoma attached to the third ventricle floor who underwent Roux-en-Y gastric bypass. He lost 38 and 59 kg at 6 and 12 months after surgery, respectively. Weight loss after bariatric surgery was as expected in this patient with severe obesity. At 6 and 12 months, brain magnetic resonance imaging (MRI) showed stability in lipoma's size.