Coligranulomatosis, which induces hepatic granulomas, and Marek's disease, one of the importantneoplastic diseases in poultry, rarely causes outbreaks in turkeys. In this study, etiological diagnoseswere performed in the light of post-mortem, histopathological, microbiological, andimmunohistochemistry studies of turkeys that died in a commercial establishment in the region ofKonya. In the post-mortem examination, many grey-white foci with a diameter of 3-10 mm, whichsometimes spread from serosa to the parenchyma, were found in the liver. Mucous exudate andhyperemia were detected in all segments of the intestine. For microscopic examination, all tissueswere stained with Haematoxylin-Eosin and some selected liver tissues with Periodic Acid-Schiff,Ziehl-Neelsen, and Giemsa. Typical structures of pyogranulomas with an eosinophilic necrotic corein the liver were identified. Tumor foci formed by pleomorphic histiocyte and lymphoid cells werealso observed in the liver, spleen, and intestines (jejunum and cecum). In the selected liver andintestinal sections, a positive reaction was obtained in tumor cells in immunohistochemical stainingwith the primary antibody specific for Marek's disease virus. In addition, Escherichia coli isolationwas performed microbiologically in swaps and samples taken from lesioned areas of the liver. As aresult of the examinations, other etiological agents that may cause hepatic granulomas in the turkeyswere excluded, and coligranulomatosis and Marek's disease were diagnosed simultaneously in thisturkey flock. It was concluded that in cases in which these two diseases are observed simultaneously,the diseases might interact with each other, and casualties may increase.