Red deer, Cervus elaphus, inhabitating the bleak moors at Glen Feshie (Invernesshire), had slow growth rates, and hinds did not attain maximum body weight and condition before six years of age. Skeletal growth, as measured by jaw length, continued to slowly increase throughout life, whereas body weight and condition declined in old age. Agerelated differences in kidney fat weight explained some of the variation in age-specific fertility and mortality rates of lactating (milk) hinds. Among individuals, fertility was positively related to body weight and condition, and after controlling for these two variables, was negatively related to skeletal size. The probability of being fertile was related to age, and differed between lactating and non-lactating hinds, as well between years, independently of differences in body composition. Temporal variation in fertility at Glen Feshie, and on Rhum, was explained by changes in population size. Comparison of the weight at median fertility (0.5 probability) in five different populations indicated that spatial variation in fertility was also density-dependent. The factors affecting body weight were complex and varied between populations. Spatial and temporal variation in body weight was not density-dependent, but differences in climate may have been important. Like fertility, conception date, estimated from foetal growth, was density-dependent at Glen Feshie. Long summer growing seasons were followed by high fertility and early conceptions. Estimated gestation length and calving date were strongly related to weight loss during the shooting season, which, in turn, was related to the biomass of new heather. The factors affecting mortality at Glen Feshie differed between hinds and calves. Hind mortality, but not calf mortality, was density-dependent. Winter severity strongly affected calf mortality, but was of secondary importance among hinds.