Technical Abstract: Studies have indicated distillers grains in cattle diets may alter the shedding of Escherichia coli O157:H7 in feces, thereby increasing the E. coli O157:H7 load on the hide and ultimately on the carcass. To determine if wet distillers grains with solubles (WDGS) in the diet affected E. coli O157:H7 in growing and finishing cattle, weaned steers (n = 603) were blocked by genetic lines and weaning weight, and randomly assigned to dietary treatments (with and without WDGS). At approximately 53 days after weaning, steers were sorted into 8 pens (4 pens per treatment) with 75 to 77 steers per pen. Growing diets with 0% or 13.9% WDGS (as %DM) were fed beginning on d 0 and finishing diets with 0% or 40% WDGS were fed beginning on d 78. Hide and fecal samples were collected from each animal for enumeration and enrichment of E. coli O157:H7 from October through June. In the growing phase, the fecal prevalence for E. coli O157:H7 was twice that in animals fed diets with 13.9% WDGS (P < 0.001), but neither the percentage nor the distribution of E. coli O157:H7 enumerable samples in feces was different for the two diets. In the finishing phase, average fecal prevalence for cattle fed 40% WDGS was 14.9% compared to 1.5% for animals fed corn (P < 0.001), and hide prevalence was 32.8 and 9.2% (P < 0.001), respectively. The average percentage of fecal E. coli O157:H7 enumerable samples during the finishing phase for cattle fed 40% WDGS was 2.7% compared to 0.1% for corn (P < 0.001). The average percentage of E. coli O157:H7 enumerable hide samples was not different (1.9 vs 0.0%, P < 0.06), but the distributions of these counts were different (P < 0.05). Animals fed 40% WDGS had higher levels of generic E. coli (P < 0.001), higher pH (P < 0.001), and lower concentrations of L-lactate (P < 0.001) in their feces. Within cattle fed 40% WDGS, fecal shedding of E. coli O157:H7 was not associated with fecal pH. However, fecal shedding of E. coli O157:H7 from the cattle fed 40% WDGS was associated with lower levels of fecal generic E. coli (6.94 vs 7.06 log10 CFU per g, P < 0.05) and higher fecal concentrations of L-lactate (1.87 vs 1.39 mM, P < 0.01). These results indicate that feeding 40% WDGS (DM basis) may increase the level and prevalence of E. coli O157:H7 in feedlot cattle, although the magnitude of the difference in this study may have been affected by low prevalence in the control pens.