Résumé : Objective: To analyze the clinical, hormonal, anatomical, and molecular characteristics of Leydig cell tumors, a very rare cause of progressive hyperandrogenism in children. Study design: Description of a 9-year-old boy with isosexual precocious pseudopuberty, and of a 12-year-old girl with rapidly progressive virilization, both due to a pure Leydig cell tumor. Review of all cases of pediatric Leydig cell tumors published since 1999 (when the first somatic mutations of the luteinizing hormone receptor were described) and reporting hormonal and/or molecular data. Results: Boys (n = 24) are younger than girls (n = 12) at diagnosis (median 6.5 vs 13.0 years, P =.04). Plasma gonadotrophins are more often completely suppressed in boys (6 cases) than in girls (2 cases). Pure Leydig cell tumors are exceedingly rare in girls (2 cases), who most often have Sertoli-Leydig tumors. These tumors affect either testis equally (11 left, 13 right) but occur more often in the left ovary (8 left, 3 right). Activating mutations of the alpha-subunit of the Gs stimulatory protein have not been found in either boys or girls and activating mutations of the luteinizing hormone receptor have only been found in boys. Conclusions: Leydig cell tumors in children display clinical, hormonal, anatomical, and molecular sexual dimorphism. Copyright © 2012 Mosby Inc. All rights reserved.