In this case report, we describe the effect of ketamine infusion in a case of severe refractory complex regional pain syndrome I (CRPS I). The patient was initially diagnosed with CRPS I in her right upper extremity. Over the next 6 years, CRPS was consecutively diagnosed in her thoracic region, left upper extremity, and both lower extremities. The severity of her pain, combined with the extensive areas afflicted by CRPS, caused traumatic emotional problems for this patient. Conventional treatments, including anticonvulsants, bisphosphonates, oral steroids and opioids, topical creams, dorsal column spinal cord stimulation, spinal morphine infusion, sympathetic ganglion block, and sympathectomy, failed to provide long-term relief from pain. An N-methyl-d-aspartate (NMDA) antagonist inhibitor, ketamine, was recently suggested to be effective at resolving intractable pain. The patient was then given several infusions of intravenous ketamine. After the third infusion, the edema, discoloration, and temperature of the affected areas normalized. The patient became completely pain-free. At one-year of follow-up, the patient reported that she has not experienced any pain since the last ketamine infusion. Treatment with intravenous ketamine appeared to be effective in completely resolving intractable pain caused by severe refractory CRPS I. Future research on this treatment is needed.