Bangladesh's tribal population was enumerated at 897,828 in the 1981 census. These tribes are concentrated in the Chittagong Hill Tracts and around Mymensingh, Sylhet, and Rajshahi. They are of Sino-Tibetan descent and differ markedly in their social customs, religion, language and level of development. They speak Tibeto-Burman languages and most are Buddhist or Hindu. The four largest tribes are Chakmas, Marmas, Tipperas, Tanchangya, and Mros. Smaller groups include the Santals in Rajshahi and Dinajpur, and Khasis, Garos, and Khajons in Mymensingh and Sylhet regions.