BACKGROUND:Community Health Workers (CHWs) have a crucial role in improving health in their communities and their role is being expanded in many parts of the world. However, the effectiveness of CHWs is limited by poor training and the education of CHWs has received little scientific attention. METHODS:Our study was carried out in two districts of KwaZulu-Natal, South Africa. We developed and piloted an inexpensive (two day) training intervention covering national government priorities: HIV/AIDS, sexually transmitted disease and Tuberculosis; and Women's Sexual and Reproductive Health and Rights. Sixty-four CHWs consented to participate in the main study which measured knowledge gains using a modified Solomon design of four different testing schedules to distinguish between the effects of the intervention, testing and any interaction between intervention and testing. We also measured confidence, satisfaction and costs. RESULTS:Following the training intervention, improvements in knowledge scores were seen across topics and across districts. These changes in knowledge were statistically significant (p