It is estimated that two million tons of wastewater are discharged daily around the world. Implementation of efficient wastewater treatment systems is a major challenge in developing countries. Biological Wastewater Treatment with Activated-Sludge Process has gained prominence in Brazil for micro-fauna and pathogenic agents removal/inactivation. However, it is know that some viruses, bacteria and protozoa can resist to wastewater biological treatments continuing its environmental propagation. Rotavirus and adenovirus antigen persistence in treated sewage at the Biological Wastewater Treatment Plant of Ribeirao Preto (BWTP-RP), Sao Paulo, Brazil, was analyzed by enzyme immunoassays. Composite sewage samples were collected at the entry and exit points from the BWTP-RP, once a month from February to December in 2010. Complementary analysis of virus in Ribeirao Preto Stream (river receiving the treated sewage from BWTP-RP), was conducted. The results showed a significant decrease of rotavirus and adenovirus antigen after biological wastewater treatment (p<0.05). The results showed no significant seasonal tendency in viral antigen density in the sewage samples (p>0.05). Despite the partial removal of viruses in treated sewage, remaining adenovirus and rotavirus antigen was detected in all collected samples at exit point of BWTP-RP. Viral antigen loads reached Ribeirao Preto Stream representing a risk to public health. Rotavirus and adenovirus present very low infectious doses, so they can affect vulnerable groups, such as children living near the stream and homeless people using the stream water for various purposes. It is noteworthy that the enteric viruses and other pathogenic protozoa are currently the primary cause of morbidity and mortality related to diarrhea in Latin America and the Caribbean. Studies addressing the environmental persistence of pathogens in watercourses are hugely important in the public health sphere, especially in developing countries, where economic, social, cultural and environmental factors are favorable to population’s exposure to diarrhea-causing agents.