Papaya ringspot virus (PRSV), which has recently been identified in Australia, is the major limiting factor in papaya production worldwide. In this paper we report the development of two Australian papaya cultivars that are immune to infection with PRSV. Papaya somatic embryos were transformed via microprojectile bombardment using a construct containing an untranslatable PRSV coat protein coding region. Immunity was demonstrated by repeated inoculation in the glasshouse and eighteen months in the field. The immune lines were shown to have up to five copies of the transgene by Southern hybridisation. Northern hybridisation showed that the coat protein transcript in the immune lines appeared to be degraded; therefore, the mechanism of resistance appears to be post transcriptional gene silencing via RNA degradation. We have taken a proactive approach to control of PRSV in Australia by developing genetically engineered resistance before the Australian papaya industry has been decimated by the inevitable spread of PRSV.