Spontaneous retroperitoneal hematoma is a rare condition. We report a 78 year-old man with progressive pain in his right thigh and hip lasting one week. The pain subsequently was associated with abdominal pain in the right lower quadrant. Physical examination revealed pain to deep palpation of the area, associated with a diffuse positive rebound pain. An abdominal and pelvis CT scan showed an extensive mesenteric hematoma. During surgery, a large retroperitoneal encapsulated hematoma, without evidence of active bleeding, was found and drained. Pathology confirmed the diagnosis and was negative for cancer.