Growth performance and carcass composition of 40 Yorkshire pigs (74.8±9.9 kg or 164.9±21.8 lbs), 20 pigs from a line selected for low residual feed intake for 5 generations and 20 pigs from a control line, was observed while fed on either an ad libitum or NRC maintenance (weight-stasis) basis over a 6 week period. The aim of the latter diet treatment was to keep pigs at a constant weight for six weeks. In the ad libitum treatment, there was no difference in initial (p < 0.49) or final body weights (p < 0.65) but the low residual feed intake line consumed 9% less feed compared to the control (p < 0.08). Similarly, there was no difference in LEA (p < 0.57) but the low residual feed intake line had slightly less backfat compared to the control (p < 0.21). These same results were found from chemical analysis of the carcass, as there was no difference in protein percentage (p < 0.60), but the ad libitum low residual feed intake pigs had a slightly lower fat percentage (p < 0.21). For the weight stasis treatment, the low residual feed intake pigs weighed 3.5% more than the control (p < 0.08), despite attempts to maintain a static body weight, and consumed 7.6% less feed overall (p < 0.09). Both lines had a decrease in backfat; however, the low residual feed intake line had an increase in loin eye area while the control line had a decrease. No differences were observed in chemical carcass composition between the two lines on the weight stasis treatment. These data show that the low residual feed intake line is more efficient, with only slight differences in carcass composition.