Assessment of the public health importance of schistosomiasis mansoni is hampered by the nonspecificity of many of its disease symptoms. Parasitologic, clinical, and anamnestic data from two areas in Burundi were used to obtain estimates of the attributable fractions for different disease symptoms at both the population level and within different age strata. A large proportion of individuals had symptoms commonly associated with Schistosoma mansoni infection that were not attributable to this parasite. The clinical indicator with the best test efficiency was shown to be bloody diarrhea. At the population level, 35% of bloody diarrhea cases were attributable to S. mansoni, compared with only 9% of diarrhea cases without blood. The attributable fractions were age-dependent, and in the case of diarrhea (with and without blood), children had a higher proportion of cases attributable to S. mansoni infection than adults. The association between infection and disease symptoms also increased with the intensity of infection. The prevalence of morbidity attributable to S. mansoni was similar for all symptoms, and higher in children than adults. The estimation of attributable fractions provides a simple approach to quantify S. mansoni-related morbidity, which could also be extended to both S. haematobium and S. japonicum. Attributable fraction estimates for these three schistosome species in different endemic areas would greatly aid in the assessment of the health burden of this parasite and the effectiveness of control programs.