Background: HIV/AIDS remains a major public health challenge in sub-Saharan Africa. Despite their important role in the spread of HIV, the impact of a HIV-positive diagnosis and treatment on the sexual and reproductive behaviour of heterosexual Nigerian men is under-researched. Aim: To determine the sexual and reproductive behaviour of HIV-positive men in Kano, Nigeria in the era of antiretroviral therapy and the health care service response. Methods: A sequential, explanatory mixed methods design was used. First, a quantitative study collected and analyzed survey data on a clinic-based sample of HIV-positive men (n=270) and matched controls (n=270). This was followed by in-depth interviews with a sub-sample of survey participants (n=22) and health workers/health managers (n=5). Findings: Compared to controls, a greater proportion of HIV-positive men were sexually active (91.9% vs. 82.2%, P<0.05). However, they had reduced coital frequency, out of fear of transmission, psychological effect, energy expenditure and perceived nutrient loss. Post-diagnosis consistent condom use was higher compared to controls (18.9% vs. 13.0%, P<0.05). Lack of interest, reduced pleasure, partner’s refusal and desire to conceive were the reasons for low condom use. A smaller proportion of HIV-positive men desired more children than controls (79.3% vs. 91.1%, P<0.05) and intent to have a child within three years (57.0% vs. 67.0%, P<0.05). Being married and employed significantly predicted sexual activity among HIV-positive men. Also, marital status, religion and spousal HIV status predicted risky sexual behaviour while fertility intention was predicted by marital status and duration, religion, employment and existing children. Late diagnosis, inadequate health worker safe conception skills were evident. Conclusions: The majority of HIV-positive men were sexually active and desired to have children, but the health care service response was inadequate. The findings highlight the need for improved reproductive health education and services to reduce risky behaviour and promote safe conception