Little is known about obesity and insulin resistance in college students. Leptin is a hormone secreted by fat cells and has been shown to strongly correlate with both obesity and insulin resistance in children and adults. We investigated associations of leptin with insulin secretion and action in 119 normal-weight students aged 18-24 years. Leptin was strongly correlated with total fat mass (r = 0.67, p less than 0.001), percentage body fat (r = 0.81, p less than 0.001), and to a lesser degree Body Mass Index, or BMI, (r = 0.23, p less than 0.02). Leptin was associated with fasting insulin (Beta plus or minus SE = 0.30 plus or minus 0.06, p less than 0.001) and insulin resistance (Beta plus or minus SE = 0.41 plus or minus 0.20, p less than 0.001) independent of total fat, gender, and age, suggesting other mechanisms of leptin and insulin regulation besides obesity. Leptin resistance is present even among young and normal-weight college students. Leptin, even more so than BMI, is an important marker of adiposity and hyperinsulinemia in normal-weight college students and may potentially be used to predict type 2 diabetes. (Contains 2 tables and 1 endnote.)