Aerococcus viridans is a gram-positive, catalase and oxidase negative, microaerophylic and non-motile coccus which is rarely associated with human infections such as endocarditis, meningitis, artritis and bacteremia. We report a case of bacteremia due to A. viridans in a 61-years-old man with malignant gall bladder neoplasm. The patient underwent a surgical operation and on the 5th day of operation he had severe abdominal pain, vomiting, high fever and discharge from operation site. He was transferred to intensive care unit and blood cultures were obtained. Piperacillin-tazobactam was initiated as empirical therapy. Blood cultures performed in Bactec system (Becton Dickinson, USA) yielded catalase negative, gram-positive cocci in tetrads. The isolate was pyrrolidonyl aminopeptidase (PYR) positive and produced alfa-hemolysis on sheep blood agar. These cocci were identified as A. viridans by Vitek 2 Compact System (BioMerieux, France) and identification was confirmed by using mini API System (BioMerieux, France). Antibiotic susceptibility testing performed with Kirby-Bauer disk diffusion method revealed that the isolate was susceptible to trimethoprim-sulfamethoxazole, tigecycline and vancomycin and resistant to penicillin, ampicillin, piperacillin-tazobactam, ceftriaxone, erythromycin, clindamycin and amikacin. The patient was successfully treated with vancomycin (2 x 1 g/day) and completely recovered without complication. In conclusion, A. viridans should be suspected as an opportunistic pathogen in immunocompromised patients and these patients should be treated according to the antibiotic susceptibility test results.