Key PointsQuestionDoes the BCG vaccine have a protective association with the risk of Alzheimer disease and related dementias (ADRD)?FindingsIn this cohort study of 6467 patients with non–muscle-invasive bladder cancer, treatment with intravesical BCG vaccine was associated with a reduced risk of ADRD in the presence of death as a competing risk. However, the risk differences varied with time.MeaningThe findings of this study suggest that bladder cancer treatment with BCG vaccine was associated with decreased mortality, and decreased ADRD, independently; clinical trials are required to study its efficacy beyond treatment in patients with bladder cancer.