Abstract: Objective To analyse the epidemiologic features of an outbreak of pharyngoconjuctivitis caused by adenoviruses type 3(Ad3).Methods All cases in the outbreak were investigated for the process of illness,symptoms and infection factors.The viruses were cultured in Hep-2 cells and isolated from eye and pharynx swabs of the patients with pharyngoconjuctivitis and the viruses types were determined using restriction endonuclease analysis(REA).The neutralizing antibodies to the Ad3 in the paired sera were detected.Results The outbreak occurred among the children aged 4-5 years in a kindergarten in Shenzhen.The cases were concentrated in two classes and the attack rates were 71.8% (28/39) and 89.70%(35/39) respectively.Most of the cases displayed symptoms of the illness,with the proportion of 90.00 being high fever(>39℃);57.6% with the conjuctivitis,and 69.7% with sore throat and other symptoms in upper respiratory tract.Total of 19 strains isolated from the swabs had an identical genotype,Ad3.The virus DNA by PCR was detected and 3 strains proved belonging to Ad3a2 by the REA.Twenty four cases showed that the neutralizing antibody titers had 4 fold rising or above.The source of infection was followed up and the route of transmission was speculated to contact among the children and by respiratory tract.Conclusion The outbreak of pharyngoconjuctivitis was caused by adenovirus type 3.