Physic nut (Jatropha curcas), an important bio-fuel crop grown in the state of Tamil Nadu, India suffered heavy losses due to a root disease in 2007. The symptoms observed were yellowing, drooping and shedding of leaves, blackening and decaying of the collar region of the stem and rotting of the roots. Lasiodiplodia theobromae was isolated consistently from the diseased tissues of affected plants. Pathogenicity of L. theobromae was confirmed by artificial inoculations on 1-year-old plants. This is the first report of root rot and collar rot disease of physic nut in India.