Online Mendelian Inheritance in Man

Online Mendelian Inheritance in Man (OMIM) is a database that keeps track of all known human genes.
It list those which cause genetic disorders, and those which simply cause traits. There are about 8,000 entries for genes, and 15,000 entries for phenotypes, which are (roughly) the feature(s) caused by a person's genes.
When possible it links diseases to specific genes. It provides a useful tool for further research. OMIM is one of the databases housed in the U.S. National Center for Biotechnology Information (NCBI). People search it using the NCBI search menus.
Versions.
Mendelian Inheritance in Man was started as books in the early 1960s. The 12th edition is the most recent book. The online version, OMIM, has been available since 1987. NCBI move it to the World Wide Web in 1995. By 2004, OMIM contained more than 15,000 records.
The MIM code.
Every disease and gene is given a six digit number. The first digit in each number tells how the gene or disease is inherited (passed from one generation to the next).
If the initial digit is 1, the trait is autosomal dominant; if 2, autosomal recessive; if 3, X-linked. Each trait defined in this dictionary has a MIM number, the number from the 12th edition of MIM. The MIM number is printed in square brackets with or without an asterisk (asterisks indicate that the mode of inheritance is known; a number symbol (#) before an entry number means that the phenotype can be caused by mutation in any of two or more genes) as appropriate. For example, Pelizaeus-Merzbacher disease [MIM #312080] is an X-linked recessive disorder.
Range of MIM codes: method of inheritance 
These codes have been used in the medical literature to provide a unified index to genetic diseases.