Background/Aims: Hypothalamic hamartoma (HH) is one of the most frequent causes of organic central precocious puberty (CPP). We compared the clinical presentation and the magnetic resonance images (MRI) of 19 patients with HH aged 5.7 ± 4.1 (SD) years at the first endocrine evaluation. They had isolated CPP (group 1, n = 9), CPP plus gelastic seizures (group 2, n = 5), isolated seizures (group 3, n = 4), and 1 patient was asymptomatic. Methods/Results: All patients without neurological symptoms (group 1 and the asymptomatic patient) had pedunculated lesion (diameter 6.4 ± 3.6 (3–15) mm), suspended from the floor of the third ventricle. All patients with neurological symptoms (groups 2 and 3) had sessile lesion (diameter 18.3 ± 9.6 (10–38) mm, p = 0.0005 compared to the others), located in the interpeduncular cistern with extension to the hypothalamus. Seven patients were overweight. The growth hormone peak, free thyroxine, cortisol and prolactin concentrations, and the concomitant plasma and urinary osmolalities were normal in all the cases evaluated. The mean predicted or adult heights of 10 patients treated 5.2 ± 3.3 years for CPP with gonadotropin hormone releasing hormone (GnRH) analog were –0.3 ± 1.7 SD, similar to their target height –0.1 ± 0.9 SD. Conclusion: The clinical presentation of HH depends on its anatomy: small and pedunculated HH are associated with CPP, while large and sessile HH are associated with seizures. The hypothalamic-pituitary function in these cases is normal, which suggests that the absence of CPP is not due to gonadotropin deficiency. GnRH analog treatment preserves the growth potential in those with CPP.