A 20-year-old woman was found to have septic arthritis of the hip due to Aerococcus viridans. This organism closely resembles Streptococcus viridans, but forms gram positive tetrads rather than chains in broth media. The organism has been reported rarely to cause endocarditis and one case of osteomyelitis has been observed. To our knowledge septic arthritis due to Aerococcus viridans has not been previously reported.