Within a three week period, four cases of Campylobacter fetus infection were identified in a hospital in Los Angeles County. Three of the four patients had drunk large quantities of an identical brand of commercially available certified raw milk. Campylobacter fetus subspecies jejuni was isolated from the blood of these three patients. The fourth patient, who did not drink raw milk, had Campylobacter fetus subspecies intestinalis isolated from his blood. A telephone survey comparing cases and controls for possible risk factors associated with Campylobacter fetus infection confirmed the association with raw milk (P = 0.003). In a serologic survey, evidence suggested that Campylobacter fetus infection was associated with raw milk consumption.