Community-based treatment is recommended for endemic populations with urinary schistosomiasis; however, the optimal target group for treatment and retreatment interval have not been established. Using ultrasound, this study identified subpopulations whose lesions were most likely to respond to treatment and characterized resurgence of pathology. Ultrasound examination of 1202 infected patients was followed by chemotherapy with praziquantel. A sample of 698 patients was followed for 18 months after treatment. Nearly all types of bladder pathologies resolved after treatment, regardless of patient's age or intensity of initial infection. However, many patients' upper urinary tract pathologies (62.5%) did not resolve. During the 18-month follow-up period, reappearance of severe bladder pathologies was rare, and <10% of persons had resurgence of mild bladder pathologies. For this population, retreatment is not needed annually but might be cost effective if given several years later. Confirmation from other areas is required before general policies can be formed.