A young patient with a severe and isolated memory disorder, meeting the criteria for MCI, was followed for a period of 8 years. His overall functional level remained stable with a CDR-score at 0.5 until the last year when it dropped to 1.0. Neuropsychological testing showed severe memory deficits but otherwise normal cognitive functions. Only minimal progression was measured; however, the last testing showed impaired abstraction and executive functioning as well as discrete problems generating names of objects and people. Neuroimaging, with MRI and SPECT, was consistent with a progressive degenerative disorder, and cerebrospinal fluid levels of beta-amyloid 1-42, tau protein, and phosphorylated tau protein were characteristic of Alzheimer's disease (AD). We argue that this is a case of prodromal AD, which illustrates an extreme version of the normal course with respect to slow progression of the disease and severity of amnesia early in the course.