The authors studied the prevalence of the aggregation in common lifestyle habits, namely, cigarette smoking, alcohol drinking, and betel-nut chewing and the demographic correlates of individual aggregation in these lifestyle behaviors among young military conscripts in Taiwan. Cross-sectional screening was conducted among conscripts in southern and eastern sections of Taiwan from Aug. 1st to Dec. 31st 2001. Totally, 3913 conscripts who had more than 1 month of service were included in this multistage sampling study. Information on smoking, drinking, and betel-nut chewing habits were ascertained as part of a self-administered questionnaire completed by examinees at the service unit. Aggregation in lifestyle habits was studied by comparing the observed and expected proportions (O/E ratio) with their 95% confidence intervals (CI) for zero, one, two, and three simultaneously occurring lifestyle habits. The study results showed a significant clustering of lifestyle habits studied; the number of subjects was greater than expected in groups with two (for cigarette smoking and betel-nut chewing, O/E ratio=1.17, 95%CI=1.06-1.28), and three (O/E ratio=5.63, 95%CI=5.06-6.20) lifestyle habits. Determinants for this clustering of lifestyle habits included lower educational levels and residential area in southern and eastern sections of Taiwan. There was a significant individual aggregation in lifestyle habits including cigarette smoking, alcohol drinking, and betel-nut chewing in the health survey among young military conscripts. In addition, young military conscripts with low educational levels and residential area in southern and eastern sections of Taiwan had an apparent tendency toward the aggregation in these lifestyle habits.