Kala-azar or visceral leishmaniasis (VL) is a parasitic disease caused by Leishmania donovani. On the Indian subcontinent, it is transmitted by the sand fly, Phlebotomus argentipes. Kala-azar is found in about 88 tropical and sub-tropical countries with approximately 350 million people living in affected areas and at risk of infection. About 500,000 cases occur annually. More than 90% of the world’s VL cases are in India, Bangladesh, Nepal, Sudan, and Brazil, affecting largely the socially marginalized and the poorest communities. In the South-East Asian Region, kala-azar occurs in India, Bangladesh, and Nepal with a small focus reported in Bhutan. In this region about 200 million people are “at risk.” Fifty-two districts in India, 12 in Nepal, and 45 in Bangladesh are endemic. Most of the SEAR countries are vulnerable to the consequences of climate change. The ultimate effects of climate change are increased flooding, the breakdown of sanitation systems, increased salinity, more vector growth, and more water- and food-borne diseases, which ultimately impact human health. Environmental changes often modify the transmission patterns of vector-borne diseases. Increases in temperature due to climate change provide a better breeding environment for vectors, including the sand fly, in places where temperatures were previously below optimum, and so, a higher rate of human VL infection may result. Further research in this area is needed.