An important part of the immune system is its ability to keep itself from attacking normal cells in the body. To do this, it uses “checkpoint” proteins on T cells, which act like switches that need to be turned on or off to start an immune response. Bladder tumours take advantage of this to express immune checkpoint proteins such as PD1 or PD2 to evade immune detection and elimination. Immune checkpoint inhibitors, such as avelumab, pembrolizumab and atezolizumab can restore T cell activity leading to durable responses in some patients. Toxicities, often resembling autoimmune conditions, are organ-specific and may occur months into treatment, necessitating vigilant monitoring and early intervention. Corticosteroids remain the cornerstone for managing immune-related toxicities, supplemented by disease-modifying agents for severe cases.