Background: There is growing interest in the use of qualitative evidence to contribute to systematic reviews of the effectiveness and cost-effectiveness of interventions, particularly social interventions in preventive health. A number of approaches to qualitative synthesis, and to mixed-methods synthesis of qualitative and quantitative data, have been put forward. It is unclear to what extent different methods of synthesis may impact on the conclusions to be drawn from mixed-methods reviews. Objective: This review of interventions to promote HIV testing among men who have sex with men (MSM) included three types of evidence: effectiveness, cost-effectiveness and qualitative evidence. We aim to explore the issues encountered in utilising these three types of evidence, and the impact of using different methods of qualitative synthesis. Methods: Effectiveness and cost-effectiveness studies were synthesized narratively. The first phase of qualitative synthesis was thematic and aggregative, with the findings presented in a matrix cross-tabulated with the effectiveness and cost-effectiveness synthesis. In a second phase of synthesis, we developed interpretive constructs from the qualitative data which were used to provide a further level of insight into the findings regarding interventions. Results: The thematic synthesis identified a number of potential barriers and facilitators of uptake of HIV testing interventions among MSM. The second phase of synthesis enabled us to develop a more complete understanding of some of these factors, such as fear of status disclosure, and to illuminate effectiveness findings in more detail. Conclusions: The conclusions drawn from mixed-methods reviews may depend on the nature and extent of the synthesis of qualitative data undertaken. Different synthesis methodologies have unique contributions to make to mixed-methods systematic reviews. However, questions remain about the validity and transparency of such approaches.