This is a case of a Caucasian gentleman in his 60’s who had been treated with checkpoint inhibitor immunotherapy in the adjuvant setting. After cycle 3 he developed polyuria and polydipsia. Diabetes Mellitus and other differentials were excluded and he was diagnosed with immunotherapy induced diabetes insipidus. His immunotherapy was stopped and he was treated with a combination of prednisolone and desmopressin. The condition persisted for some months but weaning of both treatments was possible with reversal of the condition six months after initial presentation. Given the adjuvant indication, the immunotherapy was not recommenced in this case.