Staphylococcus aureus is the most clinically important Staphylococcus species and is associated with high mortality in patients with positive blood cultures. S. aureus bacteria may cause a variety of disease manifestations ranging from minor skin infections to life-threatening conditions such as pneumonia, meningitis, osteomyelitis, endocarditis, toxic shock syndrome (TSS) and sepsis. This microorganism belonging to the gram positive cocci may also be part of the normal flora. In Sweden, penicillinase-stable penicillins are the primary alternatives to treat S. aureus infection. Mutations in genes encoding the penicillin binding proteins (PBP2) in the bacteria which lead to a lower affinity for the  beta-lactam antibiotics define  methicillin resistant S. aureus (MRSA) which is a significant global health problem. Other resistance mechanisms of S. aureus are present, and one of these is penicillinase production which is associated with resistance to penicillin G. In order to detect penicillinase production in S. aureus, there are several methods but the European guidelines recommend disc diffusion and the clover-leaf test for follow-up if the zone diameter for benzylpenicillin (PcG) is 26 mm or more. There are no modern Swedish studies on the prevalence of S. aureus susceptible to PcG and this has recently attained interest from infectious disease physicans. Thus, the purpose of this study was to investigate the frequency of S. aureus susceptible to PcG from blood cultures isolated during 2012 from the Kalmar county.    Disc diffusion testing showed that 32% of 90 unique isolates tested had an inhibition zone diameter of PcG that was ≥ 26 mm in diameter. All of these isolates were confirmed as PcG sensitive with clover-leaf test. Internal controls showed little variation and external control isolates showed full agreement with the results obtained from a Danish study, suggesting that PcG zone diameter of ≥ 26 mm in combination with cloverleaf test can be used to detect penicillin susceptibility of S. aureus.    In conclusion, this study shows that nearly 1 /3 of the blood culture isolates of S. aureus from Kalmar are sensitive to benzylpenicillin.