Hedgehog signaling is suggested to be a major oncogenic pathway in medulloblastoma, which arises from aberrant development of cerebellar granule progenitors. Allelic loss of chromosome 17p has also been described as the most frequent genetic defect in this human neoplasia. This observation raises the question of a possible interplay between 17p deletion and the Hedgehog tumorigenic pathway. Here, we identify the human orthologue of mouse REN(KCTD11), previously reported to be expressed in differentiating and low proliferating neuroblasts. Human REN(KCTD11) maps to 17p13.2 and displays allelic deletion as well as significantly reduced expression in medulloblastoma. REN(KCTD11) inhibits medulloblastoma cell proliferation and colony formation in vitro and suppresses xenograft tumor growth in vivo. REN(KCTD11) seems to inhibit medulloblastoma growth by negatively regulating the Hedgehog pathway because it antagonizes the Gli-mediated transactivation of Hedgehog target genes, by affecting Gli1 nuclear transfer, and its growth inhibitory activity is impaired by Gli1 inactivation. Therefore, we identify REN(KCTD11) as a suppressor of Hedgehog signaling and suggest that its inactivation might lead to a deregulation of the tumor-promoting Hedgehog pathway in medulloblastoma.