A 46-year-old woman presented to the ophthalmology clinic with a 7-day history of pain, redness, tearing, photophobia, and blurring of vision in both eyes. The visual acuity was 20/60 in the right eye and 20/30 in the left eye. Two months earlier, she had started treatment with atezolizumab, an antibody against PD-L1 (programmed death ligand 1), for metastatic bladder cancer. Slit-lamp examination showed conjunctival redness, pseudomembrane formation, and evidence of corneal epithelial damage in both eyes (left eye shown in Panel A). Fluorescein staining showed signs of epithelial breakdown and overlying defect in the cornea (Panel B). Culture of a corneal swab was negative, and a polymerase-chain-reaction assay was negative for herpes simplex virus. Autoimmune keratitis was suspected, so treatment with topical prednisolone was started and atezolizumab was stopped. One week after the initiation of treatment, the visual acuity had improved to 20/20 in both eyes and the corneal epithelium showed signs of healing. Atezolizumab was restarted for three more cycles, while the patient continued to receive topical prednisolone. She had no recurrence of keratitis at the 3-month follow-up.