Despite progress in increasing uptake of HIV testing and treatment, preventing new HIV infections remains a challenge for South Africa. Though in the last decade interest has grown in interventions using sport to promote health, rigorous evidence supporting the effectiveness of these interventions is limited. Also, although there is some evidence that SMS-based interventions can effectively promote healthy behaviour, few evaluations have been carried out. In 2012, a three-year cluster-randomised trial was launched to assess the effectiveness of a sport-based HIV prevention (SBHP) intervention and associated SMS campaign. The trial enrolled 46 schools in informal settlements in Cape Town and Port Elizabeth. Schools were randomised to receive the SBHP intervention or standard life-orientation classes only, with intervention schools randomised to receive (or not receive) biweekly SMS’s reinforcing the intervention. Self-administered questionnaires were completed on touchscreen mobile phones at baseline (n=4485) and midline (8-11 months post-intervention, n=3442) to assess the intervention’s effectiveness in reducing reported sexual risk behaviour and improving HIV-related knowledge and reported attitudes. Random-effects logistic and linear regression was used to assess differences between study groups at midline, adjusting for age, site, school-level clustering and baseline prevalences. Very strong evidence of a positive effect of the intervention was observed on HIV-related knowledge (β=0.39, 95%CI=0.25-0.53) among males and females and on reported HIV testing in the last year (OR=1.47, 95%CI=1.13-1.90) among males. There was, however, strong evidence of a negative effect on reported multiple partners in the last six months among males (OR=1.34, 95%CI=1.08-1.66) and on reported perpetration of intimate-partner violence by males (OR=1.27, 95%CI=1.00-1.60). There was strong evidence of that including SMS’s in the intervention reduced reported multiple partners in the last six months (OR=0.75, 95%CI=0.58-0.96). The midline results suggested the SBHP intervention was not effective in achieving its primary behavioural objectives but did improve HIV-related knowledge and HIV testing uptake among males. They provided further evidence that SMS’s may be an effective sexual health promotion tool. Further qualitative research is investigating why the intervention may have led to an increase in certain risk behaviours.