Acute septic arthritis is an orthopedic emergency that requires rapid diagnosis and treatment to prevent serious complications, morbidity, and mortality. Delayed or inadequate treatment can lead to irreversible joint damage. Risk factors for septic arthritis include previous joint pathologies like rheumatoid arthritis and crystal arthropathy, joint prostheses, low socioeconomic status, and diabetes. Given the increasing frequency of cases of septic arthritis infected with resistant and rare microorganisms, knowing regional epidemiological data is important and necessary for planning treatment approaches. The aim of this article is to present a case of bilateral knee septic arthritis caused by Bacillus spp. as a pathogen. The blood parameters and joint fluid culture of the patient led to the diagnosis of bilateral septic arthritis. In the differential diagnosis of a hot and swollen joint, especially in the presence of risk factors, septic arthritis should be considered until ruled out. It should not be forgotten that opportunistic pathogens can also cause septic arthritis.