Simple hematoma evacuation is often performed in cases of chronic subdural hematoma (CSDH) associated with arachnoid cysts (ACs) on the same side after head injury. However, it is not clear which procedure is appropriate when ACs and CSDH are located on different sides. Here, we present a case of a 3‑year‑old boy with right frontal–temporal subdural hematoma and an AC over the left frontal–temporal region. Treatment involved craniotomy with hematoma evacuation, but no drainage of contralateral AC was applied. The patient was discharged 7 days after surgery without any neurologic deficits and no symptoms of headache or poor appetite. These results suggest that craniotomy and hematoma evacuation without intervention for the AC is adequate in patients with contralateral CSDH with a large AC.