Eight subjects with late-life depression, eight subjects with probable Alzheimer disease, and eight healthy age-matched controls were studied using 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography in the resting state with their eyes open and ears unoccduded. The depressed subjects showed widespread reductions in the regional cerebral metabolic rate for glucose in most major neocortical, subcortical, and paralimbic regions that were signiScantly different from control values (P < 0.01). The metabolic decrements in the depressed group were comparable in magnitude to those seen in the Alzheimer dLwase group. These data demonstrate widespread nonfocal decline in glucose metabolism in late-life depression that is comparable to the hypometabolism seen in Alzheimer disease. These findings have pathophysiological impLications in major depressive disorder in the elderly.Depressive illness is one of the most common mental disorders in the elderly (1, 2). It typically presents as a pervasive disturbance of mood associated with neurovegetative and cognitive signs and symptoms such as disturbance of sleep and appetite, crying spells, fatigue, anhedonia, and loss of attention, concentration, and memory (1, 2). The prevalence of major depressive illness-the most severe form of the disorder-is estimated to be -1% in studies of noninstitutionalized elderly subjects (3). The prevalence of dysthymic disorder and depressive symptoms-less severe but clinically significant forms ofdepression in the same population-is 2-3 and 10-15%, respectively (3). Depression in the elderly is often associated with functional and economic loss, physical illness, institutionalization, and a high rate of suicide (1,2). Despite these staggering consequences, late-life depression remains one of the most underdiagnosed and undertreated conditions in the elderly (1, 2).While the structural basis of late-life depression has been investigated using computerized tomography and magnetic resonance imaging (4-9), there have been very few studies aimed at elucidating the physiologic basis of late-life depression (10, 11). Cerebral blood flow has been examined using the xenon-133 inhalation technique and single photon emission computed tomography (SPECT) in a mixed sample of elderly and younger subjects with major depression and in a small group of subjects with late-life depression (10, 11). Global reduction in blood flow, in the major neocortical regions, has been reported to occur in these subjects when compared to healthy age-matched controls (10). However, given the technical limitations of the xenon-133 technique, only cortical blood flow was examined by this method (10). The question of subcortical, paralimbic, and cerebellar physiological activity in subjects with late-life depression remains unanswered (10). Semiquantitative estimates of blood flowThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely t...