Johnson et al. (2010) reported a 66 % reduction in transport losses in pigs raised in large pen configurations that were pre-sorted, however, the researchers could not determine if the transport loss reduction was from the result of pre-sorting, pen size, or a combination of both factors. Therefore, the factors of pen size and pre-sorting where separately investigated in two current trials. The objective of the first experiment was to determine the effect of pre-sorting on stress responses and transport losses in market weight pigs. Although pre-sorted pigs had lower stress responses at the time of loading, there was no difference in stress responses or transport losses between pre-sorted and not pre-sorted pigs at the harvest facility. The objective of the second experiment was to determine the grow-to-finish pen size effects on the stress responses and transport losses in the market weight pig. At loading, pigs from small pens showed lower stress responses, however; at unloading pigs from small pens had a greater incidence of skin discoloration than their large pen counterparts. There were no differences observed in the present study for any transport loss measures between pigs originating from large and small pen sizes.