The study aims to explore gender differences in smoking and drinking in three Asian cities—Hanoi, Shanghai and Taipei, and assesses the magnitude of these gender differences across cities. A total of 17,016 adolescents and young adults, aged 15 to 24 years, residing in both urban and rural area of Hanoi, Shanghai and Taipei were selected by multistage sampling methods and surveyed by face to face interview. The gender differences are significant for smoking-only, drinking-only, and both behaviors in each city. With respect to smoking-only, males are more than 30.66 times as likely to report it compared with females in Hanoi, followed by Shanghai and Taipei. The above trend holds true when further examining drinking-only and both smoking and drinking. The magnitude of gender differences in smoking-only, drinking-only, and both behaviors widely vary across the three cities. Future research is needed to further examine the mechanisms behind these gender differences and how these differences may be utilized to prevent and reduce smoking and drinking in the adolescent and young adult population.