PURPOSE: Little is known about the traits of decaffeinated coffee drinkers, who are sometimes used to ascertain whether the health effects of coffee intake are due to caffeine or some other coffee ingredient. METHODS: We studied these traits in 12,467 persons who reported type of coffee consumed at health examinations; 36% drank caffeinated only, 13% drank decaffeinated only, 27% drank both types and 24% drank no coffee. RESULTS: Odds ratios estimated from logistic regression analyses revealed that compared with regular (caffeinated) coffee drinkers or abstainers, decaffeinated coffee drinkers were less likely to be heavy coffee drinkers, smokers, alcohol drinkers, users of caffeinated soft drinks and medication and to be free of illness. Increased decaffeinated coffee drinking was associated with older age, female sex, African American ethnicity, use of special diets and cardiovascular, gastrointestinal, or neuropsychiatric symptoms. Persons on special diets were more likely to drink decaffeinated coffee whether they had heart disease or were free of any illness. CONCLUSION: These data suggest that decaffeinated coffee use is related to illness in some persons but to a healthy lifestyle in others. These potential and possibly conflicting confounding factors need to be considered when studying the health effects of coffee or caffeine.