Huanglongbing (HLB) was previously known in many countries as greening disease. It is caused by the bacterium ‘Candidatus Liberibacter asiaticus’ and is vectored by the Asian citrus psyllid Diaphorina citri (Hemiptera: Psyllidae). A delimiting survey showed that the disease had become established in, and near the border town of, Vanimo in the Sandaun Province of Papua New Guinea (PNG) by late 2002. A campaign of quarantine containment and public awareness followed. A second survey undertaken 1 year later indicated that long-distance movement of the disease and its vector had not occurred. Out of a total of 120 trees indexed by polymerase chain reaction (PCR), 4/72 were HLB-positive in 2002 compared to 12/48 in 2003. The second survey found presumptive evidence for limited HLB disease cluster expansion and further independent introduction of infected planting material. HLB-positive samples were also screened for Citrus tristeza virus (CTV) infection using a double antibody sandwich enzyme-linked immunosorbent assay. The symptoms observed on leaves of orange (Citrus sinensis) and lemon (Citrus limon) infected by ‘Ca. L. asiaticus’ alone and ‘Ca. L. asiaticus’ plus CTV were similar. This is also the first verified record of CTV in PNG. No evidence was found for the presence of HLB in four Pacific Island countries (Cook Islands, Fiji Islands, Samoa and Tonga) to the east of PNG with 18 citrus trees tested negative by PCR.