Five giraffe (Giraffa camelopardalis) died peracutely within an 8-yr period. The giraffe were maintained in an outside enclosure during the day and moved under shelter at night. All the deaths occurred in winter. All the dead giraffe had serous fat atrophy at postmortem. The giraffe were fed good quantities of browse, together with alfalfa hay and commercial supplements. Retrospective analysis of the dietary ingredients showed that the diets were energy deficient. Subsequent additional high-energy feeds have caused a marked increase in surviving giraffe body weights although energy levels consumed were at the lower end of current recommendations. The relationship between low-energy reserves, high-energy demand in colder temperatures, and the possibility that hypoglycemia is a credible cause of the collapse of giraffe in these circumstances, is postulated to be the likely pathogenesis of giraffe deaths, previously reported elsewhere under the generic term "peracute mortality syndrome".