Reporting of condom-use can limit researchers' understanding of high-risk sexual behaviours. We compared self-reported condom-use with the Yc-DNA biomarker data and investigated potential factors influencing participation in, and reporting of, sexual behaviours. Self-reported data were collected using Audio Computer Assisted Self Interviews (ACASI) and samples for Yc-DNA biomarker were collected using self-administered and health worker-collected vaginal swabs from 644 women (aged 15-24 years) who were not living with HIV. Yc-DNA results and interview data were compared using McNemar-Bowker Analysis and Cohen's Kappa. Test statistics for Yc-DNA biomarker were calculated. Log Binomial models for Yc-DNA and self-reported results were conducted to assess for association. We found strong evidence (p < 0.001) for a difference between Yc-DNA and self-reported results. 13.7% of participants reported consistent condom-use with all partners, regardless of HIV status. Self-reported condom-use was discordant in 50.0% (n = 206) of cases, when compared to Yc-DNA results. Positive Yc-DNA results were found to be associated with older age (RR 1.36; 95%CI 1.04, 1.76 p = 0.023). Self-reported condom-use with partners with unknown HIV status was associated with higher education (RR 0.76; 95%CI 0.58,0.99 p = 0.043). Sensitivity analysis did not determine difference between methods for controlling for missing data. We found significant under-reporting of condomless sex in the self-reported data when compared to Yc-DNA results.