In nails various pathological changes caused by infectious agents are very often observed. Among infections of nails the most commonly occurring are those caused by fungi, which might represent up to 50% of all nail disorders, and due to the anxiety of onychomycosis, patients with nail changes report to see a dermatologist. Dermatophyte onychomycosis is definitely the most frequent fungal nail infection. Onychomycoses caused by yeasts of Candida genus occur rarely. Among onychomycoses caused by moulds in Central Europe, infections of the toe nails are caused almost exclusively by the mould Scopulariopsis brevicaulis. In nails bacterial infections caused mainly by Staphylococcus aureus, Pseudomonas aeruginosa and warts caused by HPV (human papilloma virus) may also be observed. Infections of nails may develop in previously unchanged nail plates, as well as in the course of other non-infectious nail disorders. Most commonly they affect nails changed by psoriasis, lichen planus and trauma. With regard to the frequent similarity of the clinical picture of different infectious and non-infectious nail disorders, and also coexistence of infectious changes and already existing nail diseases, it is very important to perform proper diagnostic examinations before starting a therapy.