At the beginning of 2005, an outbreak of ceruminous otitis has been observed in a breeders flock belonging to the Robusta Lionata breed, a native chicken breed reared in a Centre for the valorisation and conservation of native poultry breeds. The disease caused a high morbidity rate (90% of birds), whereas the mortality affected only 10% of the birds. The death of the birds was preceded by clinical signs, such as worsening of the ceruminous otitis with abundant secretion of bad-smelling cerumen, lack of appetite and depression. The otitis externa, mainly bilateral, was the only evident finding at necropsy. Laboratory examinations showed only the presence of Mycoplasma synoviae, either by isolation on culture media or by PCR, on ear and choana samples. Aspergillus fumigatus was detected only in one bird. In this paper, the Authors report for the first time on an outbreak of ceruminous otitis in native chicken breeds and point out that the only pathogenic agent isolated from the birds has been Mycoplasma synoviae.