Summary: Objectives: To investigate hygiene practices of caterers at large events in order to: support the production of guidance on catering at such events; to compare hygiene standards at weekends with other times in the week; and to learn lessons in preparation for the London Olympics in 2012.Study design: UK-wide study of caterers at large events, including questionnaires on hygiene procedures and microbiological examination of food, water and environmental samples.Methods: In total, 1364 samples of food, water, surface swabs and cloths were collected at 139 events, by local authority sampling officers, and transported to laboratories for microbiological analysis.Results: Eight percent of food samples were of an unsatisfactory quality, and a further 2% contained potentially hazardous levels of Bacillus spp. A significantly higher proportion of unsatisfactory food samples were taken from vendors without adequate food safety procedures in place. Fifty-two percent of water samples, 38% of swabs and 71% of cloths were also unsatisfactory. The majority of samples (57%) were collected on Saturdays, Sundays or bank holidays. Environmental swab results were significantly poorer at weekends compared with other days of the week.Conclusions: This study reinforces the fact that food hygiene is a continuing cause for concern in mobile vendors, and indicates a need for an ongoing programme of training and monitoring of caterers in preparation for the London Olympics.