Inconsistent results of the effects of dietary betaine supplementation on important economic carcass characteristics of finishing pigs have been reported. This has motivated a quantitative meta-analysis that accounted for variability among experiments. Through an extensive literature search data have been identified to evaluate the effects of dietary betaine supplementation on average daily feed intake (ADFI; 11 experiments, 18 comparisons), average daily gain (ADG; 13 experiments, 21 comparisons), backfat thickness (BFT; 10 experiments, 13 comparisons), dressing proportion (DP; 7 experiments, 10 comparisons), feed conversion ratio (FCR; 12 experiments, 18 comparisons), longissimus dorsi muscle area (LMA; 9 experiments, 13 comparisons), proportion carcass lean (PCL; 7 experiments, 10 comparisons) and tenth rib fat thickness (TRFT; 7 experiments, 10 comparisons).