Cancers of the bladder could be treated with intravesical instillation of BCG therapy. This treatment could lead to some complications. Osteoarticular ones are relatively uncommon. We describe an original observation, illustrating the development of reactive arthritis after intravesical BCG therapy. A 60-year-old man was followed for a T1G3 transitional papillary carcinoma of the bladder and was treated with intravesical BCG immunotherapy. Within the sixth intravesical instillation, he presented with polyarthritis confirmed by musculoskeletal ultrasound. The erythrocyte sedimentation rate was 100 mm without leukocytosis. The viral and bacterial serologies and immunological tests were negative. The ophthalmological examination revealed left conjunctivitis. Treatment with non-steroidal anti-inflammatory drugs was started, combined with the discontinuation of the intravesical instillation. No recurrence has been reported with a current decline of 2 years.