A single brand of homogenized milk was associated with an outbreak of Yersinia pseudotuberculosis, serotype 1B, in British Columbia. The case control study identified the same brand of homogenized milk, pork, and fruit juice as possible risk factors for illness. All case-patient stool isolates were genetic matches. A consumer sample of the brand of homogenized milk implicated by case-patients was found to be contaminated with the outbreak strain of Yersinia. An assessment of the consumer's home could not exclude the possibility of cross-contamination of the milk within the consumer's home. The traceback investigation found that this milk originated from a single plant; milk obtained from the plant showed no contamination. The precise cause of this outbreak was never determined.