The role of the sexes in incubation, their changes in body weight and associated energy costs were studied in the Wandering Albatross at South Georgia. Males incubate significantly more than females (54%, range 36–68%) and lose weight during incubation shifts at a greater absolute, but smaller proportional, rate. On average this results in both sexes losing equal proportions of body weight during typical shifts. Energy costs of incubation are calculated to lie between 1.2 and 2.0 times basal metabolism, and probably much closer to the former. All males and most females gained weight while at sea between shifts, most males doing so faster than females. On average both sexes are able at least to maintain body weight during the incubation period. More extreme individuals, however, may end incubation in poor condition and can probably redress this only by neglecting their chick. Chicks that died were more likely to have had parents with a less equal division of incubation duties.