Objective: The mainstay of distinction between prepubertal girls and girls who are suspected of having central precocious puberty (CPP) is based on gonadotropin measurements after a GnRH stimulation test to evaluate hypothalamic-pituitary-gonadal axis maturity. The objective of this study was to determine whether a single basal gonadotropin measurement carries a useful predictive value in verifying or refuting the diagnosis of CPP. Design and methods: Basal serum LH and FSH were measured by a chemiluminescent immunometric assay in a cohort of girls who had been evaluated for CPP before and after GnRH stimulation test. Peak LH levels higher than 5 IU/l were considered a pubertal response. Results: Eighty girls with suspected breast development before 8 years of age were enrolled to the study, out of whom 42 had CPP. Low basal serum LH (≤ 0.1 IU/l) was sufficient to rule out the diagnosis of CPP in 94.7% of the 38 prepubertal girls; the sensitivity of basal LH levels for this purpose was only 64%. The basal FSH and the basal LH to FSH ratio achieved less efficient predictive value with 76 and 71% sensitivity and 73 and 86% specificity respectively. Conclusion: A single basal LH measurement may be adequate to confirm but not to refute the presence of CPP in most of the girls who are evaluated for early pubertal signs.