RATIONALE: Acute calcium deposits, including acute calcific periarthritis or acute calcific peritendinitis, are benign calcifying soft tissue lesions that have a self-resolving course. These calcifying lesions usually develop in the shoulder, while acute calcific periarthritis in the digits is uncommon. When acute calcific periarthritis involves the digits, the lesion occasionally mimics other benign calcifying or ossifying lesions and can easily be misdiagnosed, resulting in unnecessary diagnostic studies and treatment. We present a rare case of acute calcific periarthritis around the proximal phalangeal joint of the left fifth finger that took a long time to spontaneously resolve, and review previous reports of similar cases. PATIENT CONCERNS: A 69-year-old woman complained of longstanding pain and swelling of the fifth finger of the left hand. She had visited several clinics and hospitals and had been treated with analgesics and splinting for more than 2 months, but the pain in the finger had gradually worsened. DIAGNOSES: Blood chemistry analysis showed no signs of inflammation or other abnormalities. Radiographs revealed a well-defined subcutaneous calcifying lesion without bony destruction, suggesting a benign calcification process. Computed tomography and magnetic resonance imaging led to a diagnosis of acute calcific periarthritis of the proximal interphalangeal joint of the fifth finger. INTERVENTIONS: An excisional biopsy was recommended to achieve a definitive diagnosis, but this was declined by the patient. Thus, no invasive treatments were administered, and she was treated with analgesics and encouraged to massage the affected finger. OUTCOMES: The pain gradually improved, and follow-up radiographs showed complete disappearance of the calcifying mass 6 months after the initial visit to our hospital, without recurrence during a follow-up period of more than 2 years. LESSONS: Acute calcific periarthritis is diagnosed based on history, clinical examination, and imaging findings, which provide evidence for the diagnosis of calcium deposition in the digits even if the lesions have been present for a long time. Watchful observation is an appropriate treatment strategy for acute calcific periarthritis of the digits.