School-based programmes to combat the spread of HIV have been demonstrated to be effective over the short-term (i.e. 6-24 months), but few studies have addressed the sustainability of such interventions. Primary School Action for Better Health (PSABH) is an intervention delivered in upper primary-school grades in Kenya using regular classroom subjects and co-curricular activities. This paper reports results of an evaluation to assess the sustainability of PSABH and its impacts three years after teachers were trained in its delivery. Twenty primary schools participated in a pre-post evaluation of PSABH in Kenya over three consecutive school years. Surveys were completed by teachers (n = 40), pupils (n = 3403), and Quality Assurance Officers (n = 15); focus groups were held with pupils, and in-depth interviews with teachers. Teachers continued to deliver programme components three years after they were trained. Gains demonstrated in pupil knowledge, attitudes and risk-reducing sexual behaviours after one-and-a-half years of programme implementation were replicated in the third year of the intervention with additional gains in attitudes related to condoms and girls' reported use of condoms. These results support the conclusion that PSABH and its impact on student knowledge, attitudes and behaviour is sustainable across at least three school years and three student cohorts. (Contains 1 note and 7 tables.)