An experiment was conducted to determine the health, welfare, and growth performance of pigs housed under optimal climatic conditions in a Specific-Stress-Free (SSF) housing system. This system was compared to a conventional housing system with the same climatic conditions. Two identical experimental rooms with five pens each were used. In each room five litters were used for the experiments. The SSF pigs were not mixed or transported, whereas the pigs in the conventional housing system were mixed at weaning and mixed and transported at 25 kg. Average daily gain for the SSF pigs was higher (P < .05) both for the rearing period and for the finishing period (P < .01). Live weight at 143 d was, therefore, higher in the SSF group (95.09 kg vs 84.8 kg, P < .001). Clinical signs were hardly seen in the SSF group, but in the control group high levels of aggression after mixing caused ear, skin, and tail lesions. Cortisol concentration of the saliva was lower in SSF pigs after weaning (P < .01). Seven and 21 d after mixing, the SSF pigs had a higher response to an intradermal injection of phytohemagglutinin (P < .001) than the control pigs. In conclusion, production performance, health, and welfare are improved when pigs are kept in an SSF housing system where they are not mixed or transported.