Aim: We present a case of autoimmune myopathy observed in a patient who developed intoleranceto intravesical Bacillus Calmette-Guerin (BCG), which is used in the treatment of non-muscle invasivebladder cancer.Case: Intravesical BCG, which is used for the treatment of non-muscle invasive bladder cancer, probablyeffects by increasing autoimmunity in the bladder. This increased autoimmunity sometimes causes localor systemic reactions. In this case report, we would like to present a 61-year-old male patient whodeveloped intolerance while taking the first dose of maintenance BCG, and then on-going treatmentwas stopped. The patient had convulsive painful cramps and muscle twitches in the left quadricepsfemoris region one month later BCG intolerance. When the patient’s anamnesis, electromyography(EMG) results, elevated Creatine Kinase value and other laboratory data were evaluated together, BCGtriggered autoimmune myopathy was considered. Therefore, steroid treatment was started and thepatient recovered seven weeks later. This is a rare case of autoimmune myopathy in a patient whoreceived intravesical BCG therapy for a bladder tumor.Conclusion: The case of BCG-associated autoimmune myopathy is extremely rare. When this situationis suspected, it is beneficial to start steroid treatment without delay.