Rognidan and Vikruti vigyan deals with the pathophysiology The one which gives pain to body is called roga, Nidana means the factors responsible for producing disease ie. etiological factors the disease. The diagnosis of the disease is also one of the important factors in Rognidan. "The science with describes roga by means of nidana, purvaroopa, roopa, samprapthi,upashaya,anupashaya,and sadhyaasadhyata is called Roganidana and Vikriti Vijnana"

This subject is a very integral part of every clinical subject. It helps to understand the disease(Vyadhi vigyanam) and it’s pathogenesis (Samprapti Vigyan), the science of Clinical examintion methods (Rugna Pariksha Vidhi), sign & symptoms or clinical features of the disease, required investigations(Vyadhi Pariksha Vidhi) and the interpretation of the results. This subject also deals with the prognosis (Sadhya-Asadhyatva) of any disease.