In 2012, the World Health Organization recommended ‘Option B+’ (lifelong antiretroviral treatment for HIV-infected pregnant women regardless of their CD4 count or WHO clinical stage) for prevention of mother-to-child transmission of HIV—based on its operational and clinical advantages. By 2015, 21 out of the 22 Global Plan priority countries had adopted the Option B+ approach. Despite its huge HIV burden, Nigeria is the only country yet to adopt Option B+. We analyse the policymaking process on Option B+ in Nigeria from 2012–2015, highlighting how factors related to the content (uncertainty about Option B+, lack of local evidence), actors (interest and power) and context (low domestic funding and poor retention in care) affected the policymaking process and present the implications of this decision for improving HIV response in Nigeria.