Intravesical instillation of bacillus Calmette-Guérin (BCG) is used in the treatment of patients with intermediate and high-risk superficial bladder carcinoma with efficacy and safety. The vast majority of patients do not present any side effects and only 5% of patients have mild and short-lived clinical manifestations such as malaise, low-grade fever, cystitis, and hematuria. Arthralgia and/or arthritis is one of the rare severe complications following intravesical BCG immunotherapy. We report here the case of a patient with reactive arthritis successfully treated with nonsteroidal anti-inflammatory drugs (NSAIDs) after the discontinuation of BCG immunotherapy.