Over a century ago Beard referred to fatigue as the ‘Central Africa of medicine – an unexplored territory which few men enter’ (Beard, 1869). The last decade has seen major advances in our understanding of chronic fatigue syndrome (CFS). Much is now known of the epidemiology, clinical features and prognosis of the condition (Wessely et al. 1998), and a number of recent papers have reported randomized trials of successful treatments involving cognitive behaviour therapy (CBT) and graded exercise (Sharpe et al. 1996; Wearden et al. 1996; Deale et al. 1997; Fulcher & White, 1997). Despite these advances, which have defined some of the broad landmarks of the illness, and improved the care of patients, many areas remain uncharted. Several papers published in this issue of Psychological Medicine take us into such unexplored territory.