In the absence of a vaccine, the global spread of COVID-19 during 2020 has necessitated non-pharmaceutical interventions to curb the rise of cases. The article uses the health belief model and a novel rapid mobile survey to examine correlates of reported mask-wearing as a non-pharmaceutical intervention in South Africa between May and August 2020.Two-way tabulations and multivariable analysis via logistic regression modeling describe correlations between reported mask-wearing and factors of interest among a sample of 7074 adults in a two-period national longitudinal survey, the National Income Dynamics Study-Coronavirus Rapid Mobile Survey (NIDS-CRAM). In line with the health belief model, results showed that self-efficacy, the prevalence of others’ mask-wearing in the same district, and affluence were positively associated with reported mask-wearing. Those who reported staying at home were significantly less likely to report wearing a mask. There was little evidence that the expected severity of the disease if contracted, affects these decisions. Hypertension, obesity, or being overweight (measured three years earlier) did not have a significant association with mask-wearing. The prevalence of mask-wearing increased significantly from May to August 2020 as COVID-19 cases increased and lockdown restrictions were eased. Contrary to the health belief model, we found that despite having a higher mortality risk, the elderly had significantly lower odds of mask-wearing. In South Africa, the mask-wearing adherence has increased rapidly. It is concerning that the elderly had lower odds of mask-wearing. This should be examined further in future research.