Although Campylobacter jejuni is now recognized as a common cause of gastroenteritis, fatalities associated with this infection in the United States have not been previously reported. Two fatalities associated with C jejuni infections occurred over a two-year period in the Denver metropolitan area. The first case was in a previously healthy 26-year-old woman who died following a two-day diarrheal illness. The second case was in a 69-year-old diabetic woman who died 19 hours after developing a gastrointestinal tract illness one day following hospital discharge for an orthopedic procedure. Both patients had taken an antimotility agent. During this same two-year period there were 24.4 reported cases of C jejuni infections per 100,000 population. The death rate per reported case was 2.4 per 1,000, and the overall death rate in the entire five-county population was 0.059 per 100,000 population. The exact causes of death for the two patients are not clear; however, hypokalemia may be a contributing factor, especially since there was no evidence of profound volume depletion in the one patient for whom laboratory data were available. Prompt hospitalization and withholding of antimotility agents may have prevented these deaths.