Congenital erythropoietic porphyria (CEP) is a rare enzymatic disorder of heme metabolism, leading to the accumulation of porphyrins in the skin and subdermal structures. We present the case of a 34-year-old, right-hand-dominant, male patient with CEP. The patient had developed a chronic open subluxation of the left index finger proximal interphalangeal joint due to skin necrosis. We successfully treated the patient with proximal interphalangeal arthrodesis. This case demonstrates that childhood-onset CEP can also manifest in the adult hand. Considering the patient's age, the destructive nature of the disease, and the poor quality of function in older patients with childhood CEP, surgical intervention was necessary to avoid further digital length loss. Although the treatment described in this case report is not uncommon, we found it essential to present this case because the clinical presentation of CEP is rare.