Skin infections caused by dermatophytes are one of the most frequent dermatological complications in patients with acquired immunodeficiency syndrome (AIDS) resulting from infection with human immunodeficiency virus (HIV). Tinea unguium associated with AIDS is characterized by being clinically more aggressive and therapeutically more difficult to treat than in the general population. Terbinafine is considered to be a first-choice option for the treatment of dermatophyte onychomycosis in immunocompetent individuals. This drug has been used in a series of 21 HIV-positive patients diagnosed with tinea unguium for 1 year in the University Hospital La Paz, Madrid. All patients underwent a subsequent clinical follow-up for 6 months. The results showed a high percentage of clinical and mycological cures, as well as maintenance of the response after follow-up; no drug interactions or significant adverse effects related to the drug under study were recorded.