In a year's study of the giraffe population of the Arusha National Park we identified 462 individuals. The cumulative first sightings of individuals were fitted to a logistic model that gave an estimated total population of 471. Immatures accounted for only 24% of the population. Twenty-two calves were born during the period of study. The giraffe of the Park are divided into ‘North’ (more precisely northeastern) and ‘South’ (southeastern) subpopulations, and although there is no barrier between them, only 3% of the population (all bulls) were ever seen in both the northern and southern parts of the Park. The northern region is further divided into four areas, each with its own assemblage of individuals, which were seldom seen elsewhere. Bulls and male juveniles were seen less often relative to their numbers than were cows and female juveniles. This indicates that they spend a greater proportion of the time in the forest than do the females. A partial list of plants eaten by giraffe in the Park is given. Acacias are an insignificant component of the diet. Calves were usually accompanied by their mothers; typically they did not lie out. Each calf was usually seen in the company of the same few individual peers. Calves spent a higher percentage of the time with calves than with their own mothers, they were closer to one another than to their mothers, and there was much physical contact between them. Bulls of each age class occurred less frequently with individuals of their own class and more frequently with bulls of other age classes than would be expected. Young bulls were frequently seen in the company of other bulls, cows and immatures, and they often engaged in sparring. Older bulls were more solitary, tended to avoid other bulls in the presence of cows and immatures, and instead of sparring they tested and courted cows. The inadequate recruitment of this senescent population is attributed mainly to low birth rate and, in the South, high mortality in the first year. A decline in numbers is anticipated.