The objectives of this experiment were to record the behaviour of group housed, male pigs over towards the end of the growth phase to examine the effect of castration. Three treatments were created: surgical castration (at 14 days of age), immuno-castration (2 doses at recommended age of 14 and 18 weeks old), and entire (un-castrated) males. Each treatment had 60 pigs. Average feed intake was highest for surgically castrated males at 17 weeks of age. Average feed intake was highest for immuno-castrated pigs at 21 weeks of age. At both 17 and 21 weeks of age, entire males had lowest feed intakes. Entire males appeared more easily distracted from feeding, thus reducing feed intake. At 21 weeks of age, immuno-castrated males had the highest live weight gains, followed by surgically castrated males. At 23 weeks of age, gains were similar to those found at 21 weeks. Entire males were more social at both 17 and 21 weeks of age. Aggression was the most predominant social behaviour observed (90 % of social behaviour), followed by mounting behaviours (10 % of social behaviour). It was presumed that live weights were higher for immuno-castrated pigs compared to entire pigs because of the effects of the immuno-castration drug, which removed certain hormones normally influencing aggression and sexual activity. Therefore, immuno-castrated pigs spent less time carrying out active aggressive and sexual behaviours, and spent more time feeding. Immuno-castrated pigs and surgically castrated pigs showed a similar reduction in social (aggressive and mounting) behaviours, and had a similar increase in feeding behaviour over entire males. Immuno-castrated pigs tended to grow faster to slaughter weight than entire males.