Mycoplasma gallisepticum is the most economically significant mycoplasmal pathogen of poultry. M. gallisepticum infections can cause significant economic losses on poultry farms from chronic respiratory disease, reduced feed efficiency, decreased growth and decreased egg production. The carcasses of birds sent to slaughter may also be downgraded. M. gallisepticum infections are notifiable to the World Organization for Animal Health (OIE). This organism has been eradicated from most commercial chicken and turkey breeding flocks in the United States; however, it remains endemic in many other poultry operations.

Since 1994, M. gallisepticum conjunctivitis has become an emerging disease in finches. This disease has been responsible for major declines in house finch populations in the eastern U.S., and was recently reported in western house finch populations. M gallisepticum can also affect other finch species, although its impact has not been as severe.