Mucopolysaccharidosis type IH (MPS IH) is a rare autosomal recessive lysosomal storage disorder. Haematopoietic stem cell transplantation (HSCT) has been proposed for the treatment of MPS IH patients and offers the possibility to grow into their adulthood. Precocious puberty has been described in few MPS patients. We report, to the best of our knowledge and for the first time, the initiation of the first waves of spermatogenesis fortuitously observed in seminiferous tubules of a pre-pubertal 19-month-old boy, affected by MPS IH and who did not present any clinical signs of precocious puberty. This patient benefited from testicular tissue cryopreservation before HSCT. Seminiferous tubule size, germ cell differentiation and Sertoli cell expression of androgen receptor and anti-müllerian hormone corresponded to the pattern observed in a pubertal boy. The Hurler syndrome may be responsible for the precocious initiation of spermatogenesis. A specific follow-up during childhood may be useful to confirm if such abnormal testis development is common in young boys with MPS IH and if it may lead to precocious onset of puberty in survivors despite HSCT. Furthermore, we have observed that Sertoli cell maturation (up-regulation of AR expression, down-regulation of AMH expression) occurred before the clinical signs of puberty and before the increase of testosterone plasmatic level.