Objective: Gonadotropin secretion was evaluated to predict hypogonadotropic hypogonadism (HH) in 36 children suspected of having HH. Methods: LH was measured for 24 h at 10-min intervals, and FSH and estradiol or testosterone at 1-hour intervals. Twenty boys (age 15.7, range 13.2–19.3 years) and 16 girls (age 16.1, range 13.0–20.6 years) were studied. Results: LH pulses were detected in 9 boys and 5 girls. HH was confirmed in all 11 LH apulsatile boys and in 8 of 11 LH apulsatile girls. Random FSH values of ≤1.11 and ≤2.86 IU/l in boys and girls, respectively, discriminated patients with LH pulses from patients without (sensitivity for lack of LH pulses 97 and 100%, respectively). In boys testicular volume was not discriminatory. In 1 girl LH pulses were observed without estradiol production, suggesting LH neurosecretory dysfunction. Conclusions: Low FSH levels in adolescence are strongly related to a lack of LH pulses. Lack of LH pulses is highly suspect for HH. FSH may be a tool in the differentiation between HH and delayed puberty.