ObjectiveTomonitorthehighriskbehaviorsandotherAIDS/STIrelatedfactorsamongmenwhohavesexwithmen(MSM),especiallymalehomosexualsinmainlandChina.MethodsSelf-administratedanonymousmailsurveyswerecarriedoutin2001,andanalyzedwithSPSS.ResultsOnethousandonehundredandnineeffectivequestionnaireswerecollectedfrom30provincesandcities.MostofMSMlivedinbigormedi-um-sizedcities,havinggoodeducation,andbeingyounger.Thenumbersofsamegendersexpartnersweremorethanone.Theyoftenhadcasualsexpartnersandunprotectedintercourse.Inthelastyear,11.45%reportedhavingbeendiagnosedSTI.AmongMSMwhohavebeentestedforHIVantibody,5.45%oftestswerepositive.ConclusionsWhileSTIratehasbeenreachingahighlevel,MSMwithSTIalsohavebeeninfectedwithHIVintheMSMofmainlandChina.OthergroupshavingsexwithMSMareatgreaterriskofSTI/HIVinfection.ItisinurgentneedtopreventandcontrolSTI/AIDSinMSM.