Background: Comprehension of informed consent poses greater challenges to clinical trial participants in The Gambia because of low literacy and absence of standardised formats for writing the local languages. This thesis reports the development and evaluation of a locally developed informed consent tool that addresses these challenges. Objectives: 1. Develop and validate an audio digitised tool for assessment of comprehension of informed consent. 2. Develop a multimedia consent tool for Gambian research participants. 3. Evaluate acceptability and ease of use of the multimedia tool. 4. Assess the effectiveness of the multimedia tool compared to ‘standard’ consent among participants in a clinical trial. Methods: A 34-item questionnaire was developed and audio-recorded in three major Gambian languages. This was digitised and validated among clinical trial participants in Gambian urban and rural areas. The informed consent document of a malaria drug trial was developed into a multimedia tool which integrated video, animations and audio narrations in three major Gambian languages. Acceptability and ease of use of the tool were assessed using quantitative and qualitative methods. Participants in the drug trial were randomised to either receive consent information through the multimedia tool or ‘standard’ procedure. Participant comprehension was assessed using the digitised questionnaire at baseline and follow-up visits. Results: The questionnaire was deemed to be valid and reliable (Cronbach’s alpha: 0.73- 0.79). Majority of the participants (70%) reported that the multimedia tool was clear and easy to understand. Participants in the intervention arm had significantly higher comprehension scores than those in the control arm at baseline and follow-up visits. Higher comprehension scores were associated with being a male participant (p=0.03), resident in a peri-urban area (p=0.02) and having basic formal education (p=0.005). Male participants (OR = 0.29, 95% CI: 0.12-0.70, p=0.006) and living in a peri-urban area (OR= 0.33, 95% CI: 0.13-0.82, p=0.017) were independent predictors of comprehension. Survival analysis showed that participants in the intervention arm took longer time to drop to 50% of the baseline comprehension scores than those in the control arm (hazard ratio=0.22, 95% CI: 0.16-0.31). Conclusions: A customised multimedia tool was more effective in delivering consent information and sustaining participant comprehension than ‘standard’ consent procedure. Further research is needed to compare the tool with conventional consent method in other sub-Saharan Africa settings.