Unfortunately type 2 diabetes mellitus has its limitation particularly in its focus on severity and phenotype rather than etiology and genotype. Two sub–groups of patients are currently distinguished by presence of obesity. A new kind of body habitus is found to have type 2 diabetes mellitus whose BMI is <20.25. 120 cases of type 2 diabetes mellitus (40 cases of lean; 40 cases of non–obese, 40 cases of obese) were selected from ambulatory patients attending Medicine outpatient department and admitted patients in the medicine wards from September 2017 to August 2018. 30 (75%) cases of lean, 34 (85%) cases of non–obese and 36 (90%) cases of obese responded in treatment with oral hypoglycemic agents, and 10 (25%) cases of lean, 4 (10%) cases of non–obese and 2(5%) case responded with insulin therapy, whereas only 2 (5%) case each of non–obese and obese responded with dietary restrictions at the initiation of present study. No lean patient responded with dietary restriction alone.