Objective: To determine whether first-voided urinary LH (FV-ULH) - level measurement can adequately assess pubertal suppression as much as standard tests can. Subjects and methods: The study group included patients with central precocious puberty and rapidly progressing early puberty who received up to 3 - 4 doses of GnRHa therapy monthly and did not have adequate hormonal suppression after GnRH stimulation (90-minute LH level > 4 IU/L). Design: All of the participants underwent an LHRH test just after admission to the study. According to the stimulated peak LH levels, the patients were divided into 2 groups and followed until the end of the first year of treatment.The concordance between FV-ULH and stimulated LH levels was assessed. Results: The FV-ULH levels in patients with inadequate hormonal suppression were significantly high compared to patients with adequate hormonal suppression. FV-ULH levels were very strongly correlated with stimulated LH levels (r = 0.91). Its correlation with basal LH levels was significant (r = 0.65). However, this positive correlation was modestly weakened after the first year of treatment.The cutoff value for FV-ULH of 1.01 mlU/mL had the highest sensitivity (92.3%) and specificity (100%). Conclusion: FV-ULH levels, using more reliable and sensitive assay methods, can be used to monitor the adequacy of GnRHa therapy.