Determining the underlying causes of racial disparities in sexually transmitted infections (STIs) is important. In the USA, rates of the most common STIs range from 5 to 20 times higher for African-Americans compared to Caucasians, and the health consequences of STIs can be serious. Residential racial segregation results in very different contexts for individuals and may be an important determinant of sexual risk. The purpose of this study was to examine how segregation and race interact to impact the age trajectory of sexual risk behaviours.