We report a case of chronic chest pain wherein ultrasound-guided brachial plexus block (BPB) was effective. A 30-year-old man complained of bilateral chest pain. Laboratory and imaging studies revealed no malignant tumor, vascular or collagen disease. Intercostal nerve, epidural, phrenic nerve, and stellate ganglion blocks were ineffective. After a careful re-examination, the pain was found to be in the area of the serratus anterior muscle. Interscalene BPB significantly improved the subjective symptoms. Though this approach is used to treat pain in the upper limbs and shoulders, it can also block the long thoracic nerve innervating serratus anterior muscle. The chest pain, in this case, was speculated to be derived from the serratus anterior muscle, and the block of the long thoracic nerve was effective. The results suggest that it is worthwhile to try an interscalene BPB. It can be safely performed in outpatients with lateral chest pain of the serratus anterior muscle.