AbstractGenes that are involved in the transcription process, mitochondrial function, glycoprotein metabolism, and ubiquitination dominate the list of 21 new genes associated with X‐linked intellectual disability since the last update in 2017. The new genes were identified by sequencing of candidate genes (2), the entire X‐chromosome (2), the whole exome (15), or the whole genome (2). With these additions, 42 (21%) of the 199 named XLID syndromes and 27 (25%) of the 108 numbered nonsyndromic XLID families remain to be resolved at the molecular level. Although the pace of discovery of new XLID genes has slowed during the past 5 years, the density of genes on the X chromosome that cause intellectual disability still appears to be twice the density of intellectual disability genes on the autosomes.