The present investigation was carried out on layer flock belong to Livestock farm complex, College of Veterinary Science, Tirupati. Among 500 birds 41 birds revealed lesions suspected for Marek's disease and morphologically diagnosed on the basis of gross lesions, cytological smears and immunocytochemistry of different organs. Haematological and biochemical examination revealed significant increase in the lymphocytes count, AST, triglyceride levels and significant decrease in cholesterol levels in the Marek's disease affected birds when compared to normal birds. Clinically, birds affected with Marek's disease revealed emaciation, depression with drooping of the wings, anorexia, gasping, reduced weight gain, diarrhoea, pale combs, wattles with presence of nodules on combs, marked reduction in egg production and reduction in size of eggs. Few birds exhibited paralysis with inward curvature of the toes and death of the birds in few days after showing the clinical signs. Grossly, visceral organs (liver, heart, lungs, kidney, ovary, spleen, thymus, pancreas, proventriculus) were enlarged with presence of focal to discrete nodules. Cytological examination of the impression smears collected from the growths of the affected organs during necropsy revealed infiltration of pleomorphic lymphoid cells with thin rim of basophilic cytoplasm. Immunocytochemical staining of the smears revealed moderate to severe immunopositive reactivity for MDV antigens in the cytoplasm of the lymphoid cells.