Four of the most common viral infections affecting psittacine birds have been studied in detail: (1) avian polyomavirus, (2) proventricular dilatation disease (PDD), (3) Pacheco's disease and (4) psittacine beak and feather disease (PBFD). The Psittacine Disease Research Group, University of Georgia, has been actively involved in this research. Proventricular dilatation disease has been reported in more than 50 psittacine species and in species in other families, while PBFD affects over 40 psittacine species. The acute and chronic clinical characteristics of the diseases, pathological features, diagnosis, and transmission prevention and control, including vaccination, are described. The vaccine for avian polyomavirus is safe and effective in captive birds, and, when used in high-risk situations, vaccination against Pacheco's disease (a psittacine herpesvirus) can prevent high mortality. A safe vaccine for PBFD is being evaluated. Specific tests for viral nucleic acid (DNA probe tests) for avian polyomavirus and PBFD virus, and anti-virus antibody assays for avian polyomavirus and Pacheco's disease have been developed which will facilitate the diagnosis and monitoring of disease. The benefits and limitations of screening psittacines for disease are also discussed.