Rationale:Accessory spleen torsion is a rare cause of the acute abdomen. The complications of accessory spleen torsion, such as intestinal obstruction, are rarer. We herein report a case of colonic obstruction caused by accessory spleen torsion because of the unusual condition.Patient concerns:A 15-year-old patient presented with acute intestinal obstruction with signs of peritoneal irritation. Abdominal computed tomography (CT) and ultrasonography examinations revealed a soft tissue mass in the left midabdomen. Systemic inflammatory response syndrome (SIRS) was observed in this case.Diagnoses:The diagnosis of peritonitis and colonic obstruction secondary to accessory spleen torsion was made. Pathologic examination showed infracted splenic tissue.Interventions:We performed emergency laparotomy and found that accessory spleen torsion pressured against splenic flexure and descending colon, and caused colon obstruction. The patient underwent accessory splenectomy and enteral decompression.Outcomes:At 6 months follow-up, the patient recovered well with perfect digestion.Lessons:Accessory spleen torsion and its complications are extremely rare. This entity should be considered in differential diagnosis of acute abdomen. However, in case of acute abdomen with critical clinical situation, emergency surgical intervention is necessary for timely diagnosis and treatment.