With the shift in hog operations to housing pigs in large groups of over 100 per pen, questions have arisen as to how these pigs should be managed. Pigs in large groups have been suggested to more efficiently use space in crowded conditions, because the free space available to all pigs is greater (McGlone and Newby, 1994). McGlone and Newby (1994) also hypothesized that space could be reduced in large groups without negatively affecting production. However, a study in a strawed system did not find such an interaction (Turner et al., 2000), and studies in nonbedded systems have not provided identical space allowances to both large and small groups (McGlone and Newby, 1994; Wolter et al., 2000). Space recommendations put forth by AAFC (1993) have been based on traditional group sizes, which tend to range from 10 to 40 pigs per pen. Therefore, this study examined effects of small (18 pigs) vs. large (108 pigs) group sizes provided 0.52 m2/ pig (crowded) or 0.78 m2/pig (uncrowded) of space on production, health, behavior, and physiological variables. Eight 7-to 8-wk-long blocks, each involving 288 pigs, were completed. The average birth weight at the beginning of the study was 37.4 ± 0.26 kg. Overall, average daily gain was 1.032 kg/d and 1.077 (±0.015) kg/d for crowded and uncrowded pigs, respectively (P = 0.018). Differences between the space allowance treatments were most evident during the final week of study. Overall gain to feed ratio was also reduced (P = 0.002) in the crowded treatment. Pigs in the crowded groups spent less (P = 0.003) time eating over the 8-wk study than did pigs in noncrowded groups, but average daily feed intake did not differ (P = 0.34) between treatments. Overall, average daily gain of large-group pigs was 1.035 kg/d, whereas small group pigs gained 1.073 kg/d (±0.015; P = 0.039). Average daily gain differences between the group sizes were most evident during the first 2 wk of the study. Over the entire study, gain to feed ratio also differed, with large groups being less efficient (P = 0.005) than small groups. Although large-group pigs had poorer scores for lameness (P = 0.012) and leg scores (P = 0.02) throughout the 8-wk period, morbidity levels did not differ (P = 0.32) between the group sizes. Minimal changes in postural behavior and feeding patterns were noted in large groups. An interaction (P = 0.04) of group size and space allowance for lameness indicated that pigs housed in large groups at restricted space allowances were more susceptible to lameness. Although some behavioral variables, such as lying postures, suggest that pigs in large groups were able to use space more efficiently, overall productivity and health variables indicate that pigs in large and small groups were similarly affected by the crowding imposed in this study. Broken-line analysis of average daily gain indicated no difference in the response to crowding by pigs in large and small groups. Little support was found for reducing space allowances for pigs in large groups.