Background: Pincer nail deformity is marked by abnormal curvature of the nail plate, often causing discomfort and pain. It is commonly reported in toenails and rarely in fingernails, where it can indicate underlying pathology, including subungual tumors. Case Presentation: A 64-year-old male presented to our service with a 9-month history of acquired pincer nail deformity of the right thumb. Clinical and dermoscopic examination revealed a thickened, yellow-colored, over-curved nail plate with underlying compact hyperkeratosis. High-frequency ultrasound detected a subungual hypoechoic lesion, and an X-ray scan showed osteoarthritic changes without bone erosion. Surgical excision was performed, and showed a polypoid lesion involving the nail matrix and bed, after avulsion of the nail plate. Histopathology examination diagnosed superficial acral fibromyxoma, characterized by spindle cell proliferation in a fibro-myxoid stroma, with CD34 and CD99 immunoreactivity. Discussion: Superficial acral fibromyxoma is a rare benign tumor affecting the nail unit, and is characterized by protean clinical features, including a subungual whitish or pinkish mass distorting the nail plate, pincer nail deformity or pterygium-like aspect. Imaging and histopathology are mandatory to achieve the correct diagnosis, distinguishing it from malignant myxoid tumors. Full excision of the lesion is recommended to prevent recurrence. Conclusion: Isolated pincer nail deformity in a fingernail warrants investigation for potential subungual lesions, including superficial acral fibromyxoma.