Steroids derived from fecal (coprostanol, epicoprostanol and coprostanone) and mixed (cholesterol, cholestanol and cholestanone) sources were analyzed in 19 surface sediments collected in two samplings by gas chromatography with flame ionization detection (GC/FID) in order to provide a regional assessment of the sewage contamination in the Iguaçu and Barigui Rivers, Southern Brazil. The mean concentrations of coprostanol in the Summer (109 ± 122 mg g -1) and Winter (130 ± 116 µg g -1) seasons in 2007, with maximum value of approximately 330 mg g -1 , situate the studied sediments as heavily contaminated by sewage. Diagnostic ratios among selected compounds suggested that domestic effluents were the main source of contamination, although the contribution of manure from livestock might also be locally important. The results show that the release of raw sewage may pose a relevant threat to the environmental health of river systems when the capacity to disperse and dilute the effluents is reduced during periods of small river water flow.