Onychomycosis was diagnosed in a two-year-old girl. The infection was caused by Trichophyton rubrum, which is the most frequent cause of toenail onychomycosis. The diagnosis was confirmed by polymerase chain reaction, microscopy and culture. She was treated with orally given terbinafine and topically given amorolfine with clinical improvement at the following control visit. Onychomycosis is rare in children, but the occurrence seems to be increasing. Medical treatment can be topical, systemic or a combination of these.