The Human Gene Mutation Database (HGMD) constitutes a comprehensive core collection of data on germ-line mutations in nuclear genes underlying or associated with human inherited disease (http://www.hgmd.org). Data cataloged include single-base-pair substitutions in coding, regulatory, and splicing-relevant regions, micro-deletions and micro-insertions, indels, and triplet repeat expansions, as well as gross gene deletions, insertions, duplications, and complex rearrangements. Each mutation is entered into HGMD only once, in order to avoid confusion between recurrent and identical-by-descent lesions. By March 2012, the database contained in excess of 123,600 different lesions (HGMD Professional release 2012.1) detected in 4,514 different nuclear genes, with new entries currently accumulating at a rate in excess of 10,000 per annum. ∼6,000 of these entries constitute disease-associated and functional polymorphisms. HGMD also includes cDNA reference sequences for more than 98% of the listed genes.