Ninety-six crossbred barrows and gilts weighing 90 +/- .67 kg were used during a 21-d study to determine the effects of a hot, diurnal temperature (H; 22.5 to 35 degrees C) compared with a constant, thermoneutral temperature (TN; 20 degrees C) and the effects of sex (barrows vs gilts) on performance. A secondary objective included the determination of weight loss as a result of a 24-h fast immediately after the 21-d feeding study of commingled vs not commingled hogs of both environmental treatments (TN and H). Pigs housed in the hot, diurnal temperature gained 16.3% more slowly (P less than .001;.77 vs. .92 kg/d) than those in the constant, thermoneutral environment. Feed intake (FI) for the H pigs was 10.9% less (P less than .001; 3.01 vs 3.38 kg/d) than that for the TN pigs. The H pigs gained 17.6 g/d less and consumed 43.5 g/d less feed for every C degrees above 20 degrees C; however, no differences were observed for feed efficiency (F/G; 3.86 vs 4.19 kg for the TN and H pigs, respectively). Average daily gain and feed/gain (F/G) were not affected by sex. Likewise, no significant interactions of temperature x sex were observed for ADG, FI, or F/G. Weight loss (shrinkage) during the 24-h fast was not affected by commingling; however, the H pigs lost 17.5% more weight (P less than .05) than the TN pigs (3.82 vs 3.25%, respectively).