Using data from a survey conducted in 2003 and employing multilevel modeling, this paper examines the impact of migration and urbanization on drug abuse and casual sex in China. The results suggest that being a migrant predicts significantly higher odds of having casual sex but lower odds of drug abuse. Living in an urban place is a significant risk factor for both illicit drug use and casual sex. There are significant cross-community (primary sampling unit) variances in the random intercept component, suggesting that the likelihood of drug abuse and casual sex is influenced by where one lives. After controlling for differences in individual demographic and psychosocial characteristics, social influences, and community factors, the intracommunity correlation is higher for drug use (0.32) than for casual sex (0.11). The results of random coefficient models further suggest that the impact of migration on drug use and casual sex also varies across communities.