Large-scale internal migration in China may be an important mechanism for the spread of HIV/sexually transmitted infections (STIs) because of the risk behaviours of migrants. We conducted a self-administered survey among 724 employees of a high-end entertainment centre in Kunshan, Jiangsu Province, China. Using logistic regression, we examined the association of hometown of origin (Kunshan city, elsewhere in Jiangsu Province, or another province in China) and consecutive years living in Kunshan with measures of HIV/STI risk behaviour. We found that increased time living in Kunshan was associated with lower odds of using condoms as contraception [odds ratio (OR) = 0.78, 95% confidence interval (CI): 0.64-0.95] and consistent condom use with a casual partner (OR = 0.66, 95% CI: 0.47-0.93), after controlling for gender, marital status age and income. The odds of having had an STI were significantly lower for Kunshan natives than those originally from outside provinces (OR = 0.25, 95% CI: 0.07-0.96), but increasing years living in Kunshan was not related to lower risk for an STI. Our findings do not support the hypothesis that migrants living far from home participate in higher risk behaviour than locals. Findings suggest that adaptation to local culture over time may increase HIV/STI risk behaviours, a troublesome finding.