Cousin marriage is an important social phenomenon, as it is closely linked to the prevailing social customs and values in the community. It is one of the topics that holds significant importance in scientific research, being one of the most common patterns. Due to the lack of similar studies on this subject, the research was conducted to determine the prevalence of cousin marriage and the most common genetic diseases in the western region of Libya. Samples were collected by distributing a questionnaire at Al-Zawiya Teaching Hospital and Sabratha Hospital. The study included samples of 49 cases of consanguineous marriages, with a total rate of consanguineous marriages with genetic diseases at 32.7%. The highest rate was in the degree of kinship between children of uncles and aunts at 46.9%, followed by distant kinship at 28.6%, and finally children of cousins at 24.5%. It was also found that the highest rate of genetic diseases was asthma at 31.3%, followed by mental retardation at 18.8%, and diabetes at 12.5%. The age group of mothers (20-29) contained the largest number at 44.9%, followed by the age groups (30-39) and (40-49) at 22.4% each, and finally the age group (50-55) at 10.2%.................... Keywords:................ Consanguineous marriage, Genetic disease ,Genes.