['To test a hypothesized association between resting leptin levels (adjusted for body fat percentage) and symptoms of primary exercise addiction.', 'Cross-sectional design.', 'Habitual amateur exercisers participating in running, fitness, weight training, and biking.', 'Twenty men with exercise addiction as defined by the Exercise Addiction Inventory (EAI scores 24-30) and 20 men in an exercise control group (EAI scores 6-16) matched on body mass index.', 'Plasma leptin and sex hormones were measured in blood samples collected under fasting and resting conditions. Body composition was assessed by dual-energy x-ray absorptiometry. Eating disorder symptoms were identified by the Eating Disorder Inventory 2.', 'The exercise addiction group had significantly (P < 0.001) lower leptin levels (1.1 μg/L, SD = 1.3) than controls (4.3 μg/L, SD = 2.9). Even when adjusted for body fat percentage, the addiction group had significantly (P < 0.001) lower leptin levels (0.1 μg/L, SD = 0.1) than the controls (0.2 μg/L, SD = 0.1). Body fat-adjusted leptin correlated with free bioavailable testosterone, but it was only significant in nonaddictive exercisers. None of the exercisers seemed to suffer from an eating disorder.'] Is exercise addiction in men associated with lower fat-adjusted leptin levels?