Carnation (Dianthus caryophyllus L.) is a cut flower with greater stipulation in the world cut flower market. In India, carnations are cultivated under polyhouses in Nilgiris and Kodaikanal districts in the state of Tamil Nadu. Carnations cultivation is impeded by various diseases, among them stem rot caused by Sclerotinia sclerotiorum (Lib.) de Bary was found to be predominant in all varieties. Survey among commercially cultivated varieties of carnation during 2013, revealed the occurrence of stem rot incited by Sclerotinia sclerotiorum, for the first time in India. The pathogen was identified as Sclerotinia sclerotiorum on the basis of phenotypic and genotypic characteristics. Carpogenic germination was induced artificially, and life cycle of the fungi was studied. Microscopic studies of the apothecium revealed the presence of spermatia, croziers, paraphyses as well as monomorphic ascospores specific to S. sclerotiorum.