PurposeTo evaluate the incidence, diagnosis and treatment of immune-related adverse events (e-irAE) of checkpoint inhibition (ICI) in metastatic urothelial carcinoma (mUC) and metastatic renal cell carcinoma (mRCC).MethodsA retrospective, single-center study was conducted to identify a cohort that received ICI for mUC or mRCC. e-irAE were classified according to the CTCAE V.5.0. Patients received ICI for mUC or mCC between 01/2017 and 03/2021. A retrospective chart review was performed. T-Test, the chi-squared test, and Fisher's exact test were performed.Results102 Patients received ICI [mUC: 40 (39%), mRCC: 62 (61%)]. 64 (63%) received an ICI monotherapy, 27 (27%) a dual ICI therapy, 11 (11%) a combination with VEGFi. e-irAE occurred in 19 (19%) patients [grade 1-2: 17 (84%), grade 3: 3 (16%)]. The median time until e-irAE was 42 days (range 11-211 days). 14 Patients developed thyroidism (14%), 4 (4%) a hypophysitis, 1 (1%) an adrenal insufficiency (AI). 7 patients (7%) had to discontinue ICI therapy [hypophysitis (100%), AI (100%), thyroidism (14%)]. 6 (86%) received cortisone. After a median range of 34 days 5 patients (71%) restarted ICI therapy. All patients (n = 4) with hypophysitis continued ICI [4 (100%) prednisone, 3 (75%) levothyroxine]. 11 (79%) presented with hyperthyroidism. 4 (37%) needed therapy (1 (7%) prednisone, 3 (21%) thiamazole, 2 (14%) beta blocker). The 9 (64%) patients with hypothyroidism received levothyroxine. Hypophysitis appears only on dual ICI (CTLA-4/PD-1) inhibition (p 0.007).ConclusionThis study shows the importance of adequate diagnosis and therapy of e-irAEs.