Although osteoarticular side effects of the Bacillus Calmette-Guérin (BCG) are rare compared to the number of administrations, BCG vaccination and cancer therapy are so widely used that the absolute number of cases is not negligible. Osteoarticular infection is an exceedingly rare complication of vaccination with the BCG. Intravesical BCG instillations used to treat superficial bladder cancer may cause arthralgia, reactive arthritis or osteoarticular infections. Intradermal BCG therapy used to treat a number of malignancies can cause osteoarticular infections or bilateral symmetric polyarthritis predominating in the wrists and fingers. In practice, when intravesical BCG instillation is followed by arthritis, hyperthermia is unhelpful for distinguishing septic arthritis from reactive arthritis. Arguments pointing to reactive arthritis include oligo- or polyarticular involvement and onset a few weeks (as opposed to a few months) after the last instillation. Nevertheless, joint fluid examination is in order to rule out septic arthritis. BCG-induced reactive arthritis usually responds well to nonsteroidal anti-inflammatory drugs. Osteoarticular infections related to BCG therapy should be treated by rifampin, isoniazid and ethambutol for 2 months, followed by rifampin and isoniazid for 10 months.