Recently, small colony variants (SCVs) of Staphylococcus aureus causing fatal infections are increasing, but rarely reported in Korea. S. aureus, SCVs are slow growing subpopulation that cause persistent and relapsing infections. S. aureus, SCVs are frequently auxotrophic for hemin, menadione, and CO2, and are often disrupted in their electron transport activity. With S. aureus, SCVs virulence is altered by a decrease in α-toxin production and susceptibility to various antibiotics, allowing their intracellular survival. We isolated S. aureus, SCVs from the sputum of a 67 year old male with pneumonia, chronic renal failure with hemodialysis and preventive antibiotic therapy. Because S. aureus, SCVs are easily missed or misdiagnosed as normal flora in routine culture due to their atypical growth behavior and biochemical reaction, the correct identification is very important, especially when no bacteria or unusual bacteria are found in patients with persistent or relapsing infections with long term antibiotic therapy. (Korean J Clin Microbiol 2003;6(2):164-167)