Gene therapy aims to correct the disease process by restoring, modifying or enhancing cellular functions through the introduction of a functional gene into a target cell. Whilst the concept of gene therapy is simple, the practical reality of translating this new technology to the clinic has proven to be more difficult than first imagined. Recent progress in gene transfer technology has shown impressive clinical success in infants with immunodeficiency. However, two of these children have subsequently developed leukaemia as a result of insertional mutagenesis, thus, raising important questions about the safety of genetic therapeutics. This article reviews the current status of gene therapy and outlines the challenges faced by this emerging technology that holds so much promise for many suffering from catastrophic disorders.