Sheep have been proposed as a source of human verocytotoxigenic Escherichia coli infection on a number of occasions but few prevalence studies have focused on identifying rates of carriage of these pathogens in this species. The purpose of this work was to establish the frequency of excretion of E. coli of serogroups 0157, 026, 0103, 0111 and 0145 in sheep presented for slaughter in Scotland and to examine their carriage of known virulence determinants. The study involved microbiological isolation of E. coli from 1082 sheep presented for slaughter in four Scottish abattoirs between July 2005 and June 2006. Using faecal enrichment and immunomagnetic separation, the isolation rate from these samples was 3.4% for E. coli serogroup 0157, 5.2% for E. coli serogroup 026, 2.3% for E. coli serogroup 0103 and 0.1 % for E. coli serogroup O145. E. coli 0111 was not isolated. In the last month of testing, which coincided with sorbitol-fermenting E. coli 0157 (SFO157) cases in children in Scotland, all 83 recta received were screened and tested negative for SFO1 57 strains. The study found no verocytotoxin-positive strains amongst the E. coli serogroup 0103 or 0145 isolates. Verocytotoxin-positive strains were identified amongst isolates of E. coli serotypes 0157 : H7 and 026 : H11. E. coli 0157 : H7 was not isolated from samples collected between January and March, a statistically significant drop (P<0.001) in mean shedding relative to other months. There was evidence (P=0.003) of higher shedding of 0157 in adults and hoggs than in lambs. E. coli 026 : H11 was isolated throughout the year, with a statistically significant peak in shedding in the third quarter (P=0.003). The results showed that sheep presented for slaughter in Scotland may carry strains of E. coli, particularly of serogroups 0157 and 026, which can be presumed to have potential to cause human infection. They did not support a hypothesis that human cases of E. coli 0157 : H7 are higher in any particular Scottish region as a direct consequence of a higher rate of faecal carriage in sheep in that region.