The aim of this study was to describe the pathological findings in budgerigars simultaneously infected under field conditions with coccidiosis and megabacteriosis. Severe diarrhea and vomiting were observed in a budgerigar flock. Affected birds showed inappetence and loss of condition, with a flock mortality rate of 30%. At necropsy, the proventriculi and ventriculi were swollen and hyperemic, and viscous mucus and blood adhered to the mucosa. Cytological examination of Giemsa stained proventricular and ventricular tissue revealed clusters of yeast. Microscopically, mild to severe inflammatory reactions, ulcers and hemorrhage were observed in the proventriculi. Numerous large, rod shaped Macrorhabdus ornithogaster organisms had colonized the proventriculi, ventriculi and gut. The bright pink organism was easily detected in periodic acid Schiff stained sections. On microscopic examination of the feces, numerous Eimeria oocysts were observed. Histopathological examination of the gut revealed numerous coccidial organisms in epithelial cells. Eimeria dunsingi (Farr, 1960) was identified in the gut contents of the birds, based on morphological characteristics. Surviving birds were treated with amphotericin-B for megabacteriosis and with toltrazuril for coccidiosis, after which the mortalities ceased. These results demonstrated that simultaneous natural infections under field conditions can cause severe, gross histopathological lesions and high rates of mortality in birds. At the same time, this is the first report of M. ornithogaster infection in budgerigars in Turkey.