Simpson-Golabi-Behmel syndrome (SGBS, MIM #312870) is an X-linked overgrowth disorder comprising multiple congenital anomalies and increased risk for embryonal tumors, mainly Wilms tumor, hepatoblastoma and neuroblastoma [1-6]. It is characterized by pre- and postnatal overgrowth, visceral and skeletal anomalies, coarse face, macroglossia, supernumerary nipples, congenital heart defects and hypotonia. In some SGBS patients mutations/deletions of GPC3 localized at Xq26 have been observed [9-11]. We have evaluated 27 patients from the Spanish Overgrowth Syndrome Registry (who fulfil clinical criteria for SGBS) for both mutations and deletions of the GPC3 and deletions of GPC4 using a combination of MLPA and direct sequence analysis. Among them we found 9 patients with abnormalities on the GPC3 gene and 18 patients who did not have any aberration on these genes This result raised the possibility that those patients might have mutations of the OFD1 gene at the Xp22 region, so we conducted a mutation analysis of this gene through direct bi-directional sequencing of the 23 exons using specific primers and comparing with the published sequence. We found that none of the 18 patient presented deleterious mutations of the OFD1 gene. Our work confirms that a substantial proportion of patients with SGBS phenotype still remains without a molecularly proven cause of the disease.