X-Linked intellectual disability accounts for a significant fraction of males with cognitive impairment. Many of these males present with a non-syndromic phenotype and presently mutations in 17 X-linked genes are associated with these patients. Mutations in IL1RAPL1 have been found in multiple families with non-syndromic X-linked intellectual disability. All of the published mutations predict loss of function of the protein. We have identified an additional two families with deletions of a portion of the gene that give rise to cognitive impairment, as well as some behavioral problems and mild dysmorphism. Our clinical findings better delineate the phenotypic spectrum associated with IL1RAPL1 mutations. © 2011 Wiley-Liss, Inc.