Quebecers of Haitian origin (QHO) have the highest HIV prevalence of all immigrant groups in the province. We conducted a study among QHO to document the behavioural risk factors for HIV transmission. Male respondents were significantly more likely than female respondents to have at least one casual heterosexual partner in the past 12 months (39.7 vs. 18.8%, p < 0.001). Males were more likely to have used a condom at last sexual intercourse with a casual partner (78.9 vs. 53.7%; p = 0.002). However, among men who never, casually, or rarely used condoms with their regular female partner, 27.3% did not use a condom at last sexual intercourse with a casual partner. In the multivariable logistic regression analysis, having at least one casual heterosexual partner in the past 12 months was associated with being younger than 29 years, being male, being single, and being a second-generation QHO. This study allows us to identify subgroups whose behaviours can result in greater vulnerability to HIV infection and other STIs.