Reinfection pattern among 6- to 20-year-old subjects was studied over 24 months in two Mauritanian villages of intenseSchistosoma haematobium infection after a targeted chemotherapy with praziquantel involving the whole community. Subjects received treatment according to the presence of haematuria/proteinuria and this indirect screening technique was able to identify 98–100% of the heavily infected subjects (50 + eggs/10 ml). The two villages differed with respect to their characteristics, quality of follow-up and reinfection pattern. The post-treatment 6-month cumulative incidence during the two transmission periods following the chemotherapy, estimated from a subset of 116 subjects, was 18·0% and 20·5%. Reinfection rates were higher among males (Cox-Mantel: P = 0·0015), among children 6–10 years of age than older (P = 0·0078) and among subjects with more than 50 eggs/10 ml of urine before treatment than subjects with a lower egg output (P = 0·009). A Cox proportional hazard regression model was fitted and confirmed that gender, age and pretreatment level of infection were predictors of the rate of reinfection but that there was no interaction between these predictors.