Background: Nocardiosis is a chronic sub acute suppurative infection that mainly affects lungs, however, other organs such as skin or central nervous system may also be involved. This is usually occurred in patients who have suppressed immune system. The present study was conducted on patients residing in Arak who have suffered from pulmonary infection.

Materials and Methods: For this descriptive study 600 subjects with pulmonary infection were included. Sputum was stained using modified Ziehl-Neelson technique in the paraffin agar medium. Specimens were determined using biochemical tests including gelatin, casein, and thyrosin hydrolysis. Finally, the prevalence of nocardiosis and its related factors were determined.

Results: Of 600 patients, 26 (4.33%) were revealed to have nocardia asteroides. There was no significant association between pulmonary nocardiosis and sex, age, occupation, and season.

Conclusion: Since the clinical features of pulmonary nocardiosis are similar to TB and other fungal infections of the lungs, despite different therapeutic approaches, clinical practitioners should be considered this infection and try to treat it.