To examine the relationship between leptin serum levels and pubertal development in girls with progressive central precocious puberty. We longitudinally investigated the leptin levels of 37 girls with central precocious puberty before and during treatment with the gonadotropin-releasing hormone agonist depot (leuprorelin acetate). Leptin and other hormone levels were determined by radioimmunoassay. Girls with central precocious puberty before treatment showed no significant difference in leptin levels as compared to the puberty stage at diagnosis of disease. In addition, the changes in leptin concentrations of girls with central precocious puberty during treatment were not statistically significant. In the Spearman correlation analysis of leptin levels with body mass index, bone age, chronological age, clinical pubertal signs along with luteinizing, follicle-stimulating, and estradiol hormone levels, we found that body mass index, weight, and chronological age were significantly correlated with leptin levels (p < 0.05) at both 3 and 6 months of leuprorelin treatment. Leptin levels increased with body mass index; however, this trend did not reach statistical significance at all follow-up time points. These data demonstrated that treatment with depot gonadotropin-releasing hormone agonist does not influence leptin concentrations. Serum leptin levels in patients with central precocious puberty are associated with body weight and body mass index.