Amazon parrots (Amazona aestiva aestiva;Amazona ochrocephala, n=6) from an aviary with different psittacine species (n=100) were submitted to the Clinic for Pet Animals, Reptiles, Pet- and Wild birds with the clinical picture ofa cloacal prolaps. The cloacal mucosa showed papillomas, and internal papillomatosis of parrots (IPP) was suspected. Hepatomegaly was detected in the radiographs of the clinically diseased amazon parrots, indicating the involvement of the liver in the disease process. The cloacal area was enlarged and showed higher densities in the radiographic picture. One of the amazons had an increased level of bile acids in the plasma supporting the suspicion of the involvement of the liver. Macroscopical and histological investigation of amazons with cloacal prolaps revealed a papillomic adenoma of the cloacal mucosa accompanied by varying degrees of bile duct carcinomas in the liver and adenocarcinomas of the pancreas. Herpesvirus genome was detected by nested PCR in cloacal swabs, liver, and cloacal tissue samples. Sequencing of part of the herpesvirus DNA-polymerase gene indicated 95% homology of the detected herpesviruses with the Psittacid Herpesvirus (PsHV) 1. No cytopathic herpesvirus was recovered from cloacal swabs and liver samples after up to four passages in chicken embryofibroblast cultures. Cloacal and choanal swabs, which were taken from the remaining 47 healthy amazon parrots and 5 Green-winged Macaws (Ara chloroptera) of the aviary, were negative for herpesvirus in the nested PCR. Only birds with cloacal papillomas and the Green-winged Macaws were tested positive for herpesvirus DNA in the nested PCR. We may speculate that there is correlation between the infection with PsHV-1 and the development of cloacal adenomas, adenocarcinomas in the pancreas and carcinomas of the bile ducts. Our results indicate that there may be a higher susceptibility in certain amazon species, while other species may not get infected even if housed in close contact to infected birds. A therapy approach with the immunomodulator Imiquimod did not improve the clinical disease of the birds, although circulating interferon levels were detected in serum samples of treated birds. We may speculate that in the case of already developed tumors an Imiquimod therapy may not lead to tumor regression.