Nocardia bacteria are aerobic actinomycetes causing severe infections of humans and animals. There are more than 30 species pathogenic for humans. The most frequently isolated strains include: N. nova complex, N. abscessus, N. transvalensis complex, N. farcinica, N. asteroidestyp VI (N. cyriacigeorgica), and N. brasiliensis, are responsible for a wide variety of diseases ranging from cutaneous to pulmonary and multi-organ forms. Occasionally, they can cause also brain abscess especially in immunosuppressed individuals. Immunocompromised patients are the most susceptible group. Proper identification of Nocardia bacteria is difficult. It is necessary to use molecular biology methods because new species sometimes do not show any phenotypic differences among themselves. Correct identification is necessary for the implementation of appropriate antibiotic therapy.