510 group-fed bulls of the Swedish Red and White breed were used to investigate differences in production and health when housed either in an insulated building with slatted floors in the pens or in an uninsulated building with partly littered pens. Two stocking densities, 11 versus 15 animals/pen, were studied as well, but only in the uninsulated building. The animals were fed concentrate ad lib., 0.5 kg/d of roughage, and were slaughtered at about 220 kg live weight (bull calves) or at about 420 kg live weight (bulls). The comparison between buildings showed no significant differences either in feed intake or in live weight gain. Feed conversion, if calculated as MJ metabolizable energy/kg live weight gain, was significantly poorer for bull calves (but not for bulls) in the uninsulated building. If calculated as MJ metabolizable energy/kg carcass gain, there was no significant difference in feed conversion between animals in different buildings. Animals in the uninsulated building had less fat in the carcass than the others. Bull calves had significantly more liver abscesses in the insulated building than in the other. Bulls were treated for pneumonia and interdigital phlegmon more often in the uninsulated than in the insulated building. Animals in the uninsulated building had a higher energy requirement for maintenance and activity than the others. The main reason for this was probably the difference between buildings in area per animal and pen design. The higher stocking density resulted in a lower growth rate of the bulls.