This study was a retrospective analysis of 53 adult patients with septic arthritis (SA) of the knee or hip treated during the years from 1955 to 2005 in Tottori University Hospital in Japan. Patients with postoperative infection, infection caused by trauma, and periprosthetic infection were excluded. The 50-year period between 1955 and 2005 was divided into five periods: there were 5 patients in the first decade, 9 in the second decade, 11 in the third decade, 10 in the fourth decade, and 18 in the fifth decade. All SA occurred in the knee until the fourth decade. Five cases of septic arthritis in the hip occurred in the fifth decade. In contrast to the decrease in direct infections (post intraarticular injection), hematogenous infections were observed to increase after 1986. The rate of SA caused by Staphylococcus aureus (including methicillin-resistant Staphylococcus aureus, MRSA) had been highest during the 50 years. Infections caused by MRSA, comprising 22% of all staphylococcal infection, occurred in the fifth decade. The numbers of patients with comorbid conditions such as diabetes increased during the 50-year period. This study indicated that patients with SA have been increasing in number. Furthermore, hematogenous SA has been increasing. The increase in occurrence of SA could result from increase in opportunistic infection, occurrence of SA of the hip, and increase in MRSA infection.