Systemic mycobacteriosis caused by Mycobacterium genavense was diagnosed in a 7-year-old captive lineolated parakeet (Bolborhynchus lineola). About a year before death, proventricular dilatation syndrome (PDS) was suggested, because of persistent regurgitations and intermittent diarrhoea. Necropsy examination did not show any signs typical of PDS and mycobacterioses. No caseous necrosis, but focal ulcerated overgrowth in the proventriculus, hypertrophy of intestinal mucosa and splenomegaly, was found. Primary neoplasia was suspected. The crucial examination was histopathology, which revealed changes typical of mycobacteriosis and the presence of numerous acid-fast bacilli. A real-time SYBR® Green PCR test was used and Mycobacterium genavense infection was diagnosed. The mycobacterium was also cultured on BD BACTEC™ 460TB 12B Middlebrook 7H12 medium.