Abstract: Objective The present study was conducted to investigate the pathogenic and epidemic factors of an outbreak of pharyngoconjunctival fever characterized by fever,angina,tonsillitis and con- junctival congestion after swimming among juvenile in Hohhot from July to August,2005.Methods The established clinical diagnostic standard and uniform epidemiological questionnaires were used to investigate the cases and to describe the epidemic characteristics.The epidemic factors were analyzed by Cohort study,PCR was performed on patients' pharyngeal swabs and stool samples,and serum antibodies were detected.Results There were 468 cases of pharyngoconjunctival fever,involving mostly middle and primary school students.The epidemic covered four urban districts with a peak oc- curred on August 2nd.The clinical characteristics were fever accompanied by angina,tonsillitis and conjunctivitis.The prognosis was good and no death was reported;95.05% of the patients had the his- tory of swimming.The Cohort study showed that the risk factors were associated with the pollution of swimming pools.Adenovirus infection was revealed by PCR and serological assay,and it was further confirmed to be adenovirus type 3 after performing gene sequencing on the PCR positive samples. Conclusion The pathogenic agent of pharyngoconjunctival fever breaking out in Hohhot was con- fumed to be adenovirus,and the polluted water in swimming pools was the main route of transmission.