Marek's disease (MD) is a common lymphoproliferative disease of chickens, usually characterized by
mononuclear cellular infiltration in different organs. The disease is caused by a herpes virus and is
transmissible. MD has been a common, important problem for poultry industry worldwide, as well as, in
our country, Iran. The aim of present study was to have an estimation of the incidence of MD in broiler
flocks of some major regions of chicken rearing in Tehran province (Savojbolagh, Karaj, Shahriar and
Varamin). This was implemented by 35 times visiting of some poultry slaughterhouses and thoroughly
inspection of chicken's carcasses and histopathological examination of various tissues and organs of
suspected and normal slaughtered chickens from 80 broiler flocks, that was reared in Tehran province.
Gross and microscopic examinations of chickens, in four mentioned regions, showed that 24 out of 80
flocks (30%) had been infected to different forms of the disease. This result indicated that MD has a high
incidence in broiler flocks of Tehran province. The incidence of cutaneous, visceral and mixed cutaneous
and visceral forms in these regions (four regions) was determined as 16.2%, 3.8% and 10%, respectively.
Moreover, no case of nervous and ocular forms was seen in this study. The result of the current study gives
a hint for the importance and losses behind the high incidence of the MD in broiler flocks of Tehran
province, Iran. Further detailed study on MD in broiler flocks and on the effectiveness of available MD
vaccines in reducing the incidence and losses of the disease is recommended.