Traditional Medicinal System (TMS) is one of the centuries-old practices and long-serving companions to the human kind to fight against disease and to lead a healthy life. Every indigenous people have been using their unique approaches of TMS practice where among, the Chinese, Indian and African TMSs are world-wide renowned. India has a unique Indian System of Medicines (ISM) consisting of Ayurveda, Siddha, Unani, Naturopathy and Homoeopathy. Siddhars are the saints as well as the eminent scholars, who have attained Ashta-mahasiddhi [Tamil: (Ashta-Eight; Mahasiddhi-Power)] or enlightment. They have postulated, practiced, immensely contributed and have established the concept of the Tamil medicinal system called Siddha System of Medicine (SSM). From ancient time, SSM has flourished and has been widely practiced in the southern part of India particularly in Tamil Nadu. The induction of the modern medicinal system has immensely influenced the existence of SSM and has made the SSM principles and practices undervalued/extinct. However, at present, still a considerable group of people are using the SSM as a basic health-care modality. In this context, the present scrutiny deals with the TMS history, its significance with a special reference to SSM history, Siddhars, the basic concept of SSM, its diagnostic procedures, materia medica and treatment. Conclusively, Siddha is one of the most ancient indigenous health practices despite its several thorny challenges and issues, which needs to be flagged effectively and to be preserved and revitalized in the international arena in the near future.