An unusual outbreak of avian mycobacteriosis in 46-week-old commercial brown layers is described. Reduced feed intake, gradual drop in egg production and increased mortality rate were observed in the flock housed in Northern Italy. 8 birds were humanely euthanatized and necropsied. The birds were in poor body condition, with pale, shrivelled combs, and principally presented prominent orbital lesions. Grossly, multiple, variable-sized nodular lesions were found in the intestinal wall, liver, spleen, lungs, bone marrow and conjunctiva. Histologically, both visceral and orbital lesions displayed granulomatous nature with variable numbers of acid fast bacilli. Polymerase chain reaction confirmed Mycobacterium avium as the causative agent. The peculiarity of this outbreak of mycobacteriosis regards type and age of the affected birds and the uncommon involvement of the soft orbital tissues.