Preface: mild cognitive impairment Recently, mild cognitive impairment (MCI) has become an area of particular research interest and many prominent medical journals have devoted their editorial pages to the introduction of this concept (1–4). The rationale behind the construc- tion of this term is that, on the way to a fully developed dementia syndrome, an individual usu- ally passes through a phase of impaired cognition that does not significantly disturb their social or occupational functioning. The most common graphical presentation of this concept is on an intermediate position on a cognitive continuum scale, which has normal aging as a starting point and dementia as an end point. Paradoxically, it seems that this dimensional approach to the disease has resulted in a new entity with numerous proposed classification criteria. As a result of variations in definitions and consequent discrepant reports on prognosis of MCI, it is still unclear to the broader medical audience if this entity also encompasses healthy elderly individuals and dif- ferent clinical subgroups, or if it is a potentially reversible and not necessarily progressive condi- tion. The purpose of this Supplement is to intro- duce MCI not as a formal diagnostic criterion, but as a relatively novel concept that is being investi- gated from a number of perspectives, predomin- antly as a possible early predictor or prodromal phase of Alzheimer’s disease (AD) and other dementias. This comprehensive overview of the topic opens with an article by Nilsson, who presents empirical data from the Betula project, with an aim to give more insight into the nature of memory function- ing in normal aging, which is essential to the topic of MCI. Palmer et al. discuss current concepts in this field, variations in the definitions and study designs, and the general pattern of evolution in persons with cognitive impairment. Wahlund et al. continue by discussing MCI from the perspective of a memory clinic and present their diagnostic procedure as well as differential follow-up out- comes of this population. The article by Forsell et al. then examines the prevalence of psychiatric symptoms in elderly persons with MCI in a population-based study. Small et al. and Arna´iz and Almkvist present literature concerning cogni- tive deficits in preclinical AD and concur on the most common cognitive manifestation of very early AD. Nyga˚rd’s article challenges the criterion of unimpaired activities of daily living within the MCI concept. Two subsequent papers deal with poten- tial biological markers of early AD. Andreasen et al. present the findings from their longitudinal study on cerebrospinal fluid biochemistry in MCI and show impressive figures on its potential predictive accuracy of progression to AD. In a more critical manner, Wolf et al. present a com- prehensive overview of neuroimaging methods in MCI assessment that suggests that selective atro- phy of specific brain area is a risk factor of progression to AD. This is followed by an article by Almkvist et al., which proposes a model of MCI on a small but exclusive population of nondemented mutation carriers predisposed to AD. Based on the evidence from the preceding articles, i.e. that MCI subjects are at high risk of developing AD, Jelic and Winblad discuss the rationale for the treatment of MCI and review currently established and putative treatments for AD that could be extrapolated to MCI. Wimo and Winblad then present cost-benefit calculations of such secondary prevention and interpret them in a broader pub- lic health perspective. Finally, in the closing state- ment, the Guest Editors summarize some of the main conceptual shortcomings discussed in the articles, and suggest future directions in research and clinical practice. Palmer K, Jelic V, Winblad B. Preface: mild cognitive impairment. Acta Neurol Scand 2003: 107 (Suppl. 179): 5–6. Ó Blackwell Munksgaard 2003. Katie Palmer, Vesna Jelic, Bengt Winblad Division of Geriatric Epidemiology and Medicine, Neurotec, Karolinska Institutet and Stockholm Gerontology Research Center, Stockholm, Sweden Key words: mild cognitive impairment; dementia; Alzheimer's disease; diagnostic criteria Acta Neurol Scand 2003: 107 (Suppl. 179): 5–6 Printed in UK. All rights reserved Copyright Ó Blackwell Munksgaard 2003 ACTA NEUROLOGICA SCANDINAVICA ISSN 0065-1427 5