This study examined 936 Ross-308 sex-separated broilers (468 males and 468 females) at 22 days of age. The chicks were fed with standard broiler starter diet for the first 21 days. Isonitrogenic grower diets (3045 versus 3222 kcal/kg M.E.) were offered to broilers housed in sex-separated and mixed-sex pens from days 22 to 43 during the experimental period. The final body weight of sex-separated chicks (1739.91 g) was greater than that of mixed-sex chicks (1714.81 g) at 43 days of age (P < 0.05). Neither growing method nor diet energy level had a significant effect on the body weight (except at 43 days of age) or body weight gain of broilers. However, effects of sex was significant (P < 0.01) on the body weight and body weight gain of broilers throughout the trial period. Sex-separated males were heavier than mixed-sex males at 36 and 43 days of age (P < 0.05). However, the diet energy level and growing method had no significant effect on feed consumption or the feed conversion rate (P > 0.05). Broilers consumed a high energy diet had a higher carcass yield and breast rate (%), but diet energy levels had no significant effect (P > 0.05) on the abdominal fat, liver or gizzard rates (%). The breast, liver and gizzard rates (%) of female broilers were more than those of males; the abdominal fat rate (%) was the same for both sexes. In conclusion, the final body weight of male broilers was higher in sex-separated houses when compared to mixed-sex growing.