Viral therapies for cancer therapy have many potential positive attributes. These include the ability to specifically infect targeted cells, specifically express toxic or immune-enhancing genes, and the ability to specifically replicate within a tumor cell. Despite these biological advantages, efficacy to date has been limited. A recent report demonstrates that the Sindbis virus has remarkable properties in three challenging areas of gene therapy - specificity, efficacy and delivery, suggesting that Sindbis has the potential to become an important gene therapy vector for cancer therapy.