Objectives: To examine risk factors associated with HIV and sexually transmitted infections (STIs) and experience of physical and sexual violence among sex workers in London, with a particular focus on differences in risk between migrants from Eastern Europe (EE) or the Former Soviet Union (FSU) and UK-born sex workers. Methods: The authors conducted a cross-sectional survey of sex workers born in the UK, EE or FSU (n=268), collecting behavioural data, testing for antibodies to HIV and Treponema pallidum, and testing for infection with Chlamydia trachomatis or Neisseria gonorrhoea. Findings: Migrants were younger, saw more clients, and were less likely to use contraception; few reported being coerced into sex work. Overall, prevalence of HIV was 1.1% (95% CI -0.1% to 2.4%), prevalence of syphilis was 2.2% (95% CI 0.4 to 4.0%), and prevalence of infection with chlamydia or gonorrhoea was 6.4% (95% CI 3.2% to 9.6%). Risk factors associated with any infection included having no contact with an outreach worker, age, and having a non-paying sex partner. Increased risk of physical violence from clients was associated with a history of imprisonment or arrest and having a non-paying sex partner. Conclusion: Findings suggest an association between outreach services and reduced risk of STIs and between having non-paying partners and increased risk of STIs. Findings also suggest an association between enforcement policies, such as arrest or imprisonment, and drug use and increased risk of physical violence. Interventions are needed to expand outreach, improve uptake of contraceptives for migrants, and reduce levels of violence for all women.