Using a mixed methods approach that included quality assessments, a mystery client study and qualitative research, we conducted a comprehensive evaluation of malaria Rapid Diagnostic Tests and in the private sector in 12 health centre catchment areas across Cambodia. In summary, we found that the RDTs collected from drug shops had maintained good quality and that storage and transport conditions were on the whole satisfactory. Uptake of RDTs appeared to highest in the most highly trained providers i.e. “cabinets”, and lowest in grocery shops, with pharmacies and drugs shops having some ambiguity around their role. Findings from the focus group discussions and the mystery client study suggest that some of the problems in uptake and interpretation relate to RDTs being on the margins of practice for these providers who see themselves as either providing a diagnosis and cure (pinit pchier bal) or simply selling drugs for symptomatic relief (lout tnam). Several problems with RDTs were identified in terms of their actual use, in particular relating to interpretation of results, blood safety, and problems related to the buffer and the blood collecting device. In summary this study provides a comprehensive assessment of malaria RDTs in one of the first countries to implement them in the private sector.