Unlike some forms of mortality inequality, sex differentials in England and Wales increased unequivocally during the Victorian era. A gradual reversal of this trend was observed only recently. The origin of the widened mortality gap between males and females lies in the transformation of the epidemiological landscape during the second half of the nineteenth century, from one where epidemic and endemic infectious diseases dominated, to one where chronic, degenerative conditions began to prevail. This so-called ‘epidemiological transition’ had differential impacts on males and females through time and in space, partly because mortality change was mediated by socially constructed gender roles. Research on rural and urban contrasts has shown consistent excess female mortality in youth and early adulthood. But because London did not exhibit this particular sex bias in the Victorian period, examination of internal variations in the capital offers an opportunity to explore the influence of factors that varied within the urban environment. Using life table decomposition, the article reveals that contrasts in cause-specific mortality between boys and girls and elderly men and women contributed most forcefully to overall male/female differences in life expectation at birth. Copyright © 2002 John Wiley & Sons, Ltd.