Immune checkpoint inhibitors (CPI) have proven remarkably effective in treating many types of malignancies but have been associated with significant risk for immune-related adverse events (irAEs)(1). Among these, new onset of insulindependent diabetes mellitus (DM) occurs in 0.2–1.0% of patients (2, 3) and is being seen more frequently as CPI become more widely used. However, the incidence, clinical course, and pathogenesis of CPI-associated DM (CPI-DM) are not well understood. To better understand the characteristics of CPI-DM, we analyzed VigiBase (4), the World Health Organization’s database of individual case safety reports, and detected 283 cases of new-onset DM from 2014 to April 2018 following treatment with CPI using the following preferred terms according to MedDRA (Medical Dictionary for Regulatory Activities): diabetic ketoacidosis (DKA), diabetic ketosis, type 1 diabetes mellitus, or fulminant type 1 diabetes mellitus; any one of these was sufficient to define CPI-DM. We noted a marked increase in reporting of CPI-DM over this time period, with over 50% of cases reported in 2017 (Table 1). Overall, half of the patients with DM presented in DKA (50.2%); 5.6% of all cases were also on steroids at diagnosis of DM, and 6.4% were on noninsulin diabetes medications in addition to insulin. Prior and/or subsequent cancer therapies are unknown, but no other immunomodulatory medications were reported. Onset of DM ranged from 5 to 790 days after the first dose of CPI (median 116 days, interquartile range [IQR] 58–207.5, n 5 91). Of the 54 patients for whom timing of CPI and DM onset is available, 69% developed DM while on CPI or within 1 month after cessation, 22% developed DM between 1 and 3 months later, and 9% developed DM more than 3 months after stopping CPI; maximum duration from cessation of CPI to DM onset was 247 days. CPI-DM was associated with at least one other irAE in 21% of cases and with another endocrine irAE in 8.5% of cases (thyroid, pituitary, or adrenal)(Table 1). In those who developed DM, there was a wide variability in duration of CPI, ranging from 1 to 24 doses (median 3 doses, IQR 1–7, n 5 48). The majority of cases of CPI-DM occurred in individuals treated with anti–programmed cell death 1 (anti-PD-1) monotherapy (52.7% nivolumab, 23.3% pembrolizumab), with only a small fraction having been treated with anti–programmed death-ligand 1 (anti-PD-L1) monotherapy (1.4% each for atezolizumab and durvalumab, no cases with avelumab). Seventeen percent of CPI-DM cases were treated with dual therapy, with either anti-PD-1 or anti-PD-L1 plus anti–cytotoxic T-lymphocyte–associated protein 4 (anti-CTLA4, ipilimumab; no cases reported with tremelimumab). Twelve cases of CPI-DM were found among patients treated with ipilimumab monotherapy. None of these 12 patients were previously treated with antihyperglycemic medications. They were mostly from the Americas (50%) and Europe (42%), with one case from Australia. Future characterization of cases of ipilimumab-associated DM will be important, as the only previously reported case of anti-CTLA4–associated diabetes was from Japan (5),