Complex regional pain syndrome (CRPS) is a very rare complication of transradial coronary intervention (TRI). We present the case of a 51-year-old man who suffered severe pain of the right forearm after TRI and progressed to type I CRPS. The patient had effort angina and underwent successful coronary artery stent deployment on the right coronary artery. After removing the hemostatic device, the patient had swelling and severe pain that was not relieved by analgesics. Continued pain progressed to allodynia, hyperalgesia, and hyperesthesia, which met the diagnostic criteria for CRPS. Electromyography showed no abnormalities in nerve conduction and thermography of the forearm showed temperature discrepancy between both forearms, which confirmed the diagnosis of CRPS. We treated the patient with sympathetic nerve block, but he still suffers from minor pain in the right forearm. This case demonstrates that unalleviated pain after TRI can progress to CRPS, and that thermography is a useful method to diagnose CRPS.