Atraumatic splenic rupture (ASR) is a rare condition that may be idiopathic or may occur in the setting of certain inflammatory processes, infections, malignancies, and autoimmune conditions. Here, we report a very rare case of ASR secondary to complicated diverticulitis. A 49-year-old female presented with sudden onset of severe abdominal pain on the day after discharge, following attempted non-operative treatment of perforated diverticulitis at the splenic flexure. She denied any history of trauma. Computed tomography showed new splenic subcapsular hematoma and gas consistent with splenic rupture. Exploratory laparotomy with splenectomy, distal pancreatectomy, splenic flexure resection, and end transverse colostomy was performed, and the patient recovered well. Although it is rare, ASR can be life threatening, and clinicians should be aware of its association with diverticulitis.