To get a thorough understanding of PD-1/L1 inhibitor-related hypophysitis (PD-1/L1-irH), we utilized a combination of disproportionality analysis and case analysis to comprehensively characterize the clinical features of PD-1/L1-irH. Significant signals of hypophysitis were detected for all PD-1/PD-L1 inhibitors in the FAERS (FDA Adverse Event Reporting System). As revealed by both FAERS and the case analysis, PD-1/L1-irH occurred more commonly in males, PD-1 inhibitors users and patients older than 65 years. The median onset time was 101 days in FAERS and 8 cycles in the case analysis. In the case analysis, eight late-onset PD-1/L1-irHs occurred even after a discontinuation of several months (4-15 months). As revealed in FAERS, the outcome of PD-1/L1-irH tended to be poor, generally resulting in 64.66% hospitalization and 12.59% death. Fatigue was the most prominent symptom of PD-1/L1-irH, followed by anorexia, hyponatremia, and hypotension, as revealed by the analysis of 84 cases. Meanwhile isolated adrenocorticotropic (ACTH) deficiency was particularly prevalent for PD-1/L1-irH (85.71%), while gonadal hormones or posterior pituitary hormones deficiencies were rare. Glucocorticoids were administered to almost all cases (81/84), with a physiologic or stress dosage in 61.9% of cases, and a high-dose in 26.2% of cases. Most cases (58.3%) showed a favorable tumor response before diagnosis of PD-1/L1-irH. PD-1/L1-irH may occur throughout the whole therapy period even after discontinuation. Clinicians should pay more attention to PD-1 inhibitor users, males and older patients. Early diagnosis and prompt managements are crucial for PD-1/L1-irH as its potentially life-threatening nature.