Actinomycosis is a rare, chronic, and slow-progressing bacterial infection caused by Actinomyces species. The condition's rarity, nonspecific clinical symptoms, and occasional occurrence in atypical locations often lead to delays in diagnosis, which are critical for initiating timely treatment and preventing further complications. We report the case of an 82-year-old man who initially developed pustules on the dorsum of his left hand, which gradually progressed over 15 years into an exophytic mass. Histopathological examination and culture confirmed Actinomycosis, and imaging studies revealed osteomyelitis affecting the carpal and metacarpal bones of the involved hand. Although the delayed diagnosis and treatment resulted in severe osteomyelitis, the patient responded favorably to a combination therapy of Amoxicillin and Trimethoprim-Sulfamethoxazole.