Background: Onychomycosis has been studied quite extensively, however, few reports on onychomycosis in a geriatric Korean population have been available. Objectives: The purpose of this study was to investigate the clinical features of onychomycosis in the elderly and to identify the etiological agents. Methods: 629 patients over 65 years of age had been diagnosed with onychomycosis during a 10-year period (2001-2010). The etiological agents were identified by cultures on Sabouraud``s dextrose agar with and without cycloheximide. Nondermatophytic molds and yeasts were considered as pathogens, if the identical fungal elements were observed at the initial direct microscopy and repeatedly in specimen-yielding cultures at a follow-up visit. Results: The 629 elderly patients represented 22.1% of all onychomycosis patients. Toenails were involved in 567 (90.1%) patients; fingernails in 39 (6.2%); both toenails and fingernails in 23 (3.7%). The ratio of male to female was 1.01:1. Associated systemic diseases were found in 327 (52.0%) cases. Distal and lateral subungual onychomycosis (80.2%) was the most common clinical type of onychomycosis. Organisms causing onychomycosis were dermatophytes (76.5%), yeasts (14.3%) and nondermatophyticmolds (9.2%). The most common cause of onychomycosis in the elderly was Trichophyton rubrum. Conclusion: Because of the increase in onychomycosis in the elderly, we suggest the need of a careful mycological examination in the elderly patients with onychomycosis.