Based on the findings of the IMbrave150 trial, atezolizumab+bevacizumab (atezo+beva) combination therapy is currently used as a first-line treatment for unresectable hepatocellular carcinoma (HCC) in Japan. Although atezo+beva combination therapy has proved to be useful in clinical practice, reports of immune-related adverse events (irAEs) associated with immune checkpoint inhibitors are increasing. Herein, we present three cases with pituitary adrenocortical insufficiency that occurred following atezo+beva therapy for unresectable HCC. We diagnosed pituitary adrenocortical insufficiency based on decreased serum cortisol levels and unchanged serum adrenocorticotropic hormone levels. Notably, all patients experienced a considerable improvement in hyponatremia, and their blood pressure promptly normalized with the initiation of hydrocortisone treatment. Immune checkpoint inhibitors can cause various irAEs. Of these, hyponatremia and hypotension occurred due to pituitary adrenocortical insufficiency should be kept in mind, when administering atezo+beva as part of the treatment regimen.