Under CCP 340.5, the statute of limitations on a medical malpractice claim expires at the earlier of three years from the date of injury or one year from the date of discovery. Injury from the failure to diagnose a latent, progressive condition occurs “when the undiagnosed condition develops into a more serious condition,” and that more serious condition is made manifest by an appreciable increase or alteration in symptoms. The patient’s mere suspicion does not trigger the statute of limitations when no more serious condition is manifest and no lack of diligence is shown. Here, the evidence on summary judgment left triable issues of fact as to when plaintiff’s headaches from the tumor defendants failed to diagnose increased in frequency or severity sufficiently to constitute an injury and when plaintiff discovered his injury and its negligent cause.