Deep-litter, large group systems have been developed as an alternative housing system for growing pigs. These systems are cheaper to establish and are perceived as being more welfare friendly for pigs, compared to conventional housing systems. Deep-litter, large group systems offer more pen space per pig (approximately 1 m² per pig), larger group sizes (ranging from 150 to 2000 pigs per pen), an enriched environment, (an environment which provides an outlet for rooting and foraging in deep bedding), together with the opportunity for increased social interaction among pigs (Morrison et al., 2003a,b). Conventionally, pigs are housed in more confined systems with fully, or partially slatted floors, liquid effluent system, group sizes ranging from 5 to 50 pigs with a floor space allowance of approximately 0.7 m² per pig. Anecdotal evidence suggests that pigs raised in deep-litter, large group systems are less fearful of humans and novel objects and are easier to handle when transporting. It is difficult to compare housing systems since they are often confounded by factors such as pen space, group size, environment and substrate provision. The scientific literature is deficient in information on the relationships between these factors and pig behaviour in large multi-factorial experiments. The aim of this experiment was to compare the behaviour, welfare, growth performance, and meat quality of pigs in a deep-litter, large group housing system compared to a conventional housing system. Castrated males were housed from 9 weeks of age in a conventional housing (15 pigs/pen; 1.0 m²/pig) or deep-litter, large group housing system (90 pigs/pen; 1.7 m²/pig). Behavioural observations and stress physiology measurements were conducted at 9, 17 and 22 weeks of age. The willingness of the pigs to approach a novel object was assessed using a standard novel object test at 22 weeks of age. Pigs in the deep-litter, group-housing system spent more time standing, locomoting, and interacting with their environment compared with contemporaries housed in the conventional system. At 17 weeks but not at 9 or 22 weeks, pigs in the conventional housing engaged in more social interactions than deep-litter housed pigs. Salivary cortisol was higher in deep-litter pigs compared to conventional pigs at 9 weeks of age but was similar at 17 and 22 weeks of age. Pigs in the deep-litter, large group system exhibited more exploratory behaviour compared to conventionally raised pigs in the novel test. Loins from pigs housed in the deep-litter, large group treatment had lower loin pH, more purge loss, more glucose in purge and were lighter in subjective colour than loins from conventionally housed pigs. A trained sensory panel detected no differences in tenderness, juiciness or overall desirability of loins from deep-litter or conventionally housed pigs. In this experiment, the housing system modified pig behaviour, fearfulness and stress physiology (at 9 weeks of age) but these differences did not negatively impact meat quality.