Bladder cancer is a malignant disease that ranks tenth in terms of global incidence. Its incidence is increasing, while mortality rates are decreasing due to advancements in therapy. Intravesical BCG immunotherapy has been the established and widely accepted treatment for non-muscle invasive bladder cancer for over 40 years. The etiology of bladder cancer is complex, involving exposure to various carcinogens such as tobacco, exposure to aromatic amines, various types of radiation, and genetic predisposition. Bladder cancers can be categorized into two main types: non-muscle invasive and muscle-invasive. Non-muscle invasive carcinomas are confined to the mucosal layer of the bladder and the underlying connective tissue and muscle-invasive carcinomas extend beyond the muscular layer of the bladder wall. Intravesical BCG immunotherapy has shown exceptional effectiveness in treating recurrent non-muscle invasive bladder cancer. The development of BCG therapy began forty years ago and is now considered the gold standard in the adjuvant treatment of this cancer. Treatment guidelines prescribe strict criteria for selecting patients who will derive maximum benefit from BCG therapy. BCG therapy reduces the recurrence rate by 40% compared to exclusive surgical tumor removal and has an advantage over intravesical chemotherapy for high-risk tumors. Although BCG therapy can lead to side effects, the majority of these effects are mild and can be effectively managed. Commonly reported side effects include irritation of the bladder, heightened urgency to urinate, and occasional episodes of bleeding. It is important to note that these side effects are typically of a mild nature and can be readily addressed with appropriate treatment. Continuous monitoring of patients during therapy is important to promptly recognize and address side effects. By adhering to treatment guidelines and continuously monitoring treatment efficacy, it is possible to improve outcomes in the management of bladder cancer.