We reported a case of hypophysitis caused by a programmed death-1(PD-1)inhibitor. The patient was a 59-year-old female with metastatic malignant melanoma who participated in the phase Ⅱ clinical trial of a PD-1 inhibitor toripalimab. More than five months after the administration of toripalimab, she experienced fatigue, depression, nausea, and anorexia. Laboratory examinations showed mild hyponatremia, secondary adrenal insufficiency, and secondary hypothyroidism. MRI revealed the enlargement of her pituitary with obvious enhancement. The patient was diagnosed as hypophysitis caused by the PD-1 inhibitor and was given replacement therapy with physiological doses of corticosteroid and levothyroxine sodium. Her symptoms were then improved. MRI revealed that her pituitary size returned to normal after 8 weeks of treatment and remained stable during every 3-month follow-up. This case reminds us of the possibility of hypophysitis when patients suffere from fatigue and anorexia during the process of PD-1 inhibitor treatment. Correct diagnosis, proper therapy, and regular follow-up are important to ensure the patients′ safety, and to improve their prognosis.