The aim of this study was to assess the effect of transmission on the outcome of treatment of urinary schistosomiasis given in two different transmission seasons (high and low) among schoolchildren in the urban and peri-urban areas of Matola and Maputo, southern Mozambique. The results of this study are presented in six chapters. Chapter one provides background information on urinary schistosomiasis. In chapter two, information on the study area, study design and methodology are provided. Chapter three describes the Schistosoma haematobium transmission pattern in the study area. In chapter four, information on the epidemiology and morbidity of S. haematobium infection in the study area is given. Chapter five provides information about the effect of transmission season on the outcome of treatment in terms of cure rate, reinfection, resolution and reappearance of ultrasonographically detectable bladder pathology. Chapter six gives information of the effect of treatment on anthropometric indices. In chapter seven, overall discussion of the findings and recommendations for future studies are provided and in chapter eight the main conclusions and the impact of the results for the national Mozambican schistosomiasis programme are presented.