Developments in genomic microarray technology have revolutionized the study of human genomic copy number variation. This has significantly affected many areas in human genetics, including the field of X-linked mental retardation (XLMR). Chromosome X-specific bacterial artificial chromosomes microarrays have been developed to specifically test this chromosome with a resolution of approximately 100 kilobases. Application of these microarrays in X-linked mental retardation studies has resulted in the identification of novel X-linked mental retardation genes, copy number variation at known X-linked mental retardation genes, and copy number variations harboring as yet unidentified X-linked mental retardation genes. Further enhancements in genomic microarray analysis will soon allow the reliable analysis of all copy number variations throughout this chromosome at the kilobase or single exon resolution. In this review, we describe the developments in this field and specifically highlight the impact of these microarray studies in the field of X-linked mental retardation.