It is commonly believed that ruminants exposed to sunlight and heat stress (HS) consume more concentrate and lower forage, but there is limited evidence on this issue. The objective of this study was to determine the productivity and voluntary intake of concentrate and alfalfa hay in a cafeteria delivery method in outdoor (OUT)- vs. indoor (IN)-housed growing Afshari lambs during summer. Thirty male lambs (30.4 ± 4.6 kg) were randomly housed OUT and subjected to sunlight without any shade or kept IN under shade for a period of 42 d in a completely randomized design. The average temperature humidity index for IN and OUT environments were 69.8 and 70.7, respectively. Concentrate and alfalfa hay contained 20.9% and 15.6% CP, respectively. Feed intake (concentrate and hay separately), rectal temperature and respiration rate were measured 2 times a day at 0800 and 1530 h throughout the experiment. Although hay intake was not different between 2 groups since morning feeding until 1530 h, OUT lambs had lower concentrate intake (535 vs. 611 ± 21.7 g/d; P = 0.02). Total concentrate consumption, however, tended (P < 0.06) to be greater for OUT compared with IN lambs (1513 vs. 1418 ± 34.9 g/d), without any difference in hay intake. Accordingly, OUT treatment resulted in greater (120 ± 39.1 g/d; P < 0.04) total dry matter intake (concentrate + hay). The final BW for OUT vs. IN lambs (48.5 vs. 46.6 ± 1.2 kg; P = 0.28) was not different. Total average daily gain was less for IN lambs (369 vs. 431 ± 14.4 g/d; P = 0.01). Feed to gain ratio was not affected by treatments (5.23 vs. 4.79 ± 0.28, for IN and OUT lambs, respectively). The morning rectal temperature was influenced by treatment whereby IN animals were warmer (0.2 ± 0.04°C; P = 0.01), whereas the evening rectal temperature was higher in OUT lambs (0.2 ± 0.0 7°C; P = 0.04) and had more evening respiration rate (53 ± 3.7 more breath per minute; P = 0.01). Generally, under the conditions of the current experiment, subjecting to sunlight and HS did not result in increased concentrate intake during the hottest times of day and warrants more research in large ruminants to revise the old beliefs.