Objective To summarize the clinical features of infectious mononucleosis(IM)in aduIt patients.Methods Thirty cases of adult patients with IM were analyzed retrospectively being inDatient in Huashan Hospital from 2002 to 2007.Results Of these 30 patients with IM,male was slightly more than female with average age of 31.8 years old.Liver function of 77 percent patients were abnormal,while 70%splenomegaly,33%skin rash,20%EB virus-IgM positive and 10%hepatomegaly.Two cases were diagnosed with chronic active EB virus infection(CAEBV).Treatment strategies of IM were antiviral and symptomatically therapy.Conclusions IM diagnosis is difficult due to the variety of clinical features.CAEBV is rare in adult patients.The clinical prognosis of IM is good if treated properly.