Background Mothers living with human immunodeficiency virus (HIV) should be guided to practise safe childbirth, provide appropriate infant feeding, return infants for repeat HIV testing and administer for the required period, protective antiretroviral (ARV) medication (post-exposure prophylaxis [PEP]) to their infants. Although several studies have explored challenges related to the prevention of mother-to-child transmission (PMTCT), no studies were found that focused specifically on the mother and PEP. Objectives To explore and understand the challenges experienced by mothers in Lusaka, Zambia, whilst providing their children with PEP. Methods This study utilised a qualitative methodology and a descriptive design. Fifteen semi-structured individual interviews were conducted with mothers who gave PEP to their infants. Study evaluation made use of Creswell’s six steps of data analysis. Results Women experienced numerous challenges. Challenges of an individual and social nature included ‘negative’ emotions, misconceptions and a lack of understanding of PEP. Post-exposure prophylaxis was sometimes burdensome and partner involvement often limited. Cultural, religious practices and stigma deterred some women from continuing PEP. Healthcare challenges included time-consuming appointments and protracted waiting periods. Clinic organisation was often inefficient and complicated by stock-outs of essential medication such as nevirapine. Healthcare workers were at times stigmatising towards mothers living with HIV and their infants. The counselling support provided by the healthcare workers was felt to be inadequate in the face of the burden of PEP. Conclusion Post-exposure prophylaxis as part of the PMTCT programme is key to eliminating mother-to-child transmission of HIV. Postnatal support for women administering PEP to their children can be enhanced through counselling that is person- and family-centred is culturally sensitive and offers differentiated services that include PEP, integrated mother-and-child healthcare and access to support groups.