We report two cases of pachydermodactyly. Case 1 was a 16-year-old girl who complained of asymptomatic, bulbous, firm swellings which developed insidiously on both sides of the proximal interphalangeal (PIP) joint of her right middle finger. Case 2 was a 14-year-old boy with similar lesions on the sides of the PIP joints of the index and middle fingers of both hands. They both had histories of mild, repetitive mechanical trauma of the fingers. Radiologic findings showed soft tissue swellings without any bony or articular abnormalities. Histopathologic findings from the bulbous swellings revealed marked hyperkeratosis, slight epidermal hyperplasia, and a markedly thickened dermis with a deposition of mucinous material among the collagen fibers. Ultrastructural examinations of both cases showed decreased diameters of collagen fibrils. The lesions temporarily improved with intralesional injection of triamcinolone acetonide. Pachydermodactyly is more commonly found in boys and the affected fingers are more numerous in boys. Both of the present cases had the habit of rubbing and gripping their fingers unconsciously. Mechanical trauma of the fingers around puberty may play an important role in pachydermodactyly.