First eleven leaves not numbered / The purpose of this study was to identify, explore and describe the potential contributing factors of the upsurge of HIV among children aged three to eighteen months in the Mangaung Metropolitan area of the Free State Province in South Africa. The study was conducted at five primary healthcare facilities and one hospital in the Mangaung metropolitan municipality of the Free State Province with sixty randomly selected mothers of children testing HIV-positive for the first time between the ages of three and eighteen months. The convergent mixed-methods research design was opted for, according to which both qualitative and quantitative data were collected at the same health facilities selected by means of cluster sampling. The review of medical records, unstructured interviews, and structured questionnaires were used for qualitative and quantitative data collection, while random cluster sampling was used for participant selection. Thematic data analysis was applied for the interpretation of recurrent patterns of qualitative and quantitative data. The study results revealed that mothers were well-informed about the prevention of mother-to-child-transmission. The main factors that contributed to more children testing HIV positive after the routine tests were conducted at ten weeks included non-adherence factors to PMTCT prescripts mainly by mothers, such as: babies were not brought to the clinics for testing and immunisations at ten weeks, and that mothers acquired HIV infection during the breastfeeding period. Some other potential contributing factors were late antenatal booking which lead to the delay in initiation of antiretroviral treatment, nonadherence to antiretroviral therapy during pregnancy, and mixed feeding. The themes that emerged from the qualitative data were psychological factors, emotional factors, socioeconomic factors, missed opportunities, risky behaviour, as well as women disempowerment; while some mothers were left with unanswered questions. The results of the qualitative part complemented the quantitative findings as they uncovered the factors that led to the deviation from the PMTCT prescripts by the mothers. The study’s recommendations include PMTCT psychological assessment and counselling; partner and community involvement; women empowerment; and that couple testing at antenatal and postnatal clinics should be a national policy subjected to protracted monitoring and evaluation processes. / Health Studies / D. Litt. et Phil. (Health Studies)