A case-control study was designed using equine medical records from the UC Davis Veterinary Medical Teaching Hospital (VMTH) and data derived through a mailed survey. The objective was to evaluate the associations between horse demographics, horse-management factors, and equine Corynebacterium pseudotuberculosis infection in California. Horses admitted to the VMTH between July 1 1992 and June 30 1994 served as the study base for case identification and simple random sampling of 800 controls. A questionnaire was mailed to the owners of all horses enrolled in the study to collect data on demographics, management and health-related questions. A logistic-regression model containing age, outdoor activity level, other locations in California, insect-control measures, contact with other horses, and summer pasture was developed. The final model was adjusted for the suspected confounding variables admission type, regular teaching hospital patient and breed. Horses of age between 1 and 2 yrs and between 3 and 5 yrs, and horses in contact with other horses or horses on summer pasture had significantly increased odds (p < 0.05) of being diagnosed with C. pseudotuberculosis infection. The results support the hypotheses that the disease predominantly affects young-adult horses of all breeds and both sexes, and that management factors play an important role in occurrence of the disease. Since the existing serological test system is not reliable and destruction of infected animals is not feasible, the most-logical approach for disease prevention is the early identification and isolation of clinical cases and the implementation of management changes like improvement of stable hygiene and insect control and change of pasture practices.