This study involved direct observation of the differences in prevalence of disease and utilization of medical care by smokers, non-smokers, and ex-smokers. The data was collected from the 1989 Korean National Health Survey (1989 KNHS). A total of 5,201 individuals ages 20 to 59 were randomly selected from the whole Korean population using the three-stage stratified random sampling. Based on the logistic regression, the following results were obtained. Compared with the non-smokers, the relative risks for an acute disease were 1.9 and 1.7 for male ex-smokers and female current smokers, respectively. Smoking behavior significantly increased utilization of health services such as admissions (RR = 2.5 for current smokers) among females, outpatient visits (RR = 2.1 for ex-smokers, RR = 2.3 for age began to smoke was less than 18 years) among males and (RR = 1.5 for current smokers) among females. Furthermore, the utilization of outpatient services for ex-smokers who were self-concerned about their health was 3.4 times higher than the non-smokers. Based on the weighted least square regression model the days of medication for male current smokers and ex-smokers were significantly longer than non-smokers. These effects persisted after controlling for major identified confounding factors. Thus, the results of this study confirmed that smoking is an important cause of diseases and a major contributing factor to the use of health services.