Literature suggests that individuals may trade off health for income in face of an economic shock. Being in a close contact profession, the livelihoods of sex workers were severely affected by the COVID-19 pandemic. Few studies exist on whether prevalence of better-renumerated condomless sex increased among this population in low and middle-income countries and discuss its implications on HIV/STI transmission especially during pandemic situations. We reported cross-sectional condom use prevalence estimates of 600 female sex workers in Dakar, Senegal from data collected before (2015, 2017) and during the pandemic (June-July 2020). Condom use prevalence was elicited via list experiments for more truthful estimates. Double list experiment estimates of mean condom use prevalence declined from 78.2 percent (95% CI: 70.9-85.5 percent) in 2017 to 65.1 percent (95% CI: 57.6-72.7 percent) in 2020. This statistically significant decrease of 13.1 percentage points (p=0.014) represents a 16.8 percent fall in condom use and a 60.2 percent increase in condomless sex prevalence. The fall in condom use prevalence was largely concentrated amongst the asset-poor, providing some suggestive evidence that economic reasons drove the fall in condom use, reinforcing findings in existing literature regarding the positive relationship between economic shocks and risky sexual behaviours. At the point of the survey, the observed decline in client numbers exceeded the reduction in condom use prevalence, suggesting potential mitigation of HIV/STI transmission risks during the COVID-19 pandemic; nevertheless, the lack of direct comparability between these two metrics warrants cautious interpretation. However, more accurate epidemiological modelling considering the non-sex worker population and longer-term studies on whether condom use prevalence returned to pre-COVID levels after client numbers recovered are required for a comprehensive assessment of the pandemic’s short-term and longer-term impact on HIV/STI transmission.