Immune checkpoint inhibitors (ICIs) have demonstrated significant efficacy in the treatment of various cancers, but their use is also associated with immune-related adverse events (irAEs). While common irAEs, such as dermatitis, pneumonitis, and colitis, are well-documented, rare events like cystitis and ureteritis remain underreported. This report presents three cases of ICI-induced cystitis and ureteritis. The first case involves a 67-year-old female with lung cancer who developed immune-related cystitis and ureteritis twice—once following pembrolizumab treatment and a recurrence after treatment discontinuation. Both episodes were corticosteroid-sensitive. The second case involves a 37-year-old female with cervical cancer who developed these conditions following treatment with cadonilimab. Her symptoms improved with oral corticosteroids and intravesical corticosteroid irrigation. The third case describes a 35-year-old female with endometrial cancer who responded similarly to corticosteroid therapy after receiving pembrolizumab. This report underscores the importance of early recognition and management of rare irAEs, and highlights intravesical methylprednisolone as a potential treatment modality that warrants further investigation.