BACKGROUND: Access and adherence to artemisinin-based combination therapy (ACT) are key challenges to effective malaria treatment. A secondary analysis of the Sierra Leone malaria Knowledge, Attitudes, and Practices (mKAP) survey was conducted to investigate access and adherence to ACT for the treatment of fever in children under-five. METHODS: The mKAP was a nationally representative, two-stage cluster-sample survey, conducted in 2012. Thirty primary sampling units per district were randomly selected using probability proportionate to size, based on national census estimates; 14 households were subsequently randomly selected and enrolled per sampling unit. The analysis was restricted to children under-five with fever in the past two weeks. Factors associated with access and adherence were assessed using multivariate logistic regression. RESULTS: Of 5169 enrolled households, 1456 reported at least one child under-five with fever in the past two weeks. Of the 1641 children from these households, 982 (59.8%) received any treatment for fever and were analysed for access to ACT; 469 (47.6%) received ACT and 466 were analysed for treatment adherence. Only 222 (47.4%) febrile children received ACT and completed 3-day treatment. In an adjusted analysis, factors associated with ACT access included knowledge of ACT (odds ratio [OR] 2.78, 95% CI 2.02-3.80; p < 0.001), knowledge of insecticide-treated nets (ITNs) (OR 1.84, 95% CI 1.29-2.63; p = 0.001), source of care (public health facility vs. other; OR 1.86, 95% CI 1.27-2.72, p = 0.001), geographic region (East vs. West; OR 2.30, 95% CI 1.20-4.44; p = 0.025), and age (24-59 vs. 0-23 months; OR 1.45, 95% CI 1.07-1.96; p = 0.016). The only factor associated with ACT adherence was time to treatment; children treated within 24 h were less likely to adhere (OR 0.55, 95% CI 0.34-0.89; p = 0.015). CONCLUSIONS: In 2012, access and adherence to ACT remained low in Sierra Leone. Knowledge of ACT and ITNs, and seeking care in the public sector, were most strongly associated with ACT access. National surveys provide important information on anti-malarial access and could be expanded to measure treatment adherence.