The concept of gene therapy involves the introduction of genetic material into patient cells to cure or alleviate the symptoms of a disease by complementing a damaged gene or by giving the cell a new function. The belief that gene therapy would soon reach the clinic has been widely spread, frequently resulting in controversies when these expectations were not met. Nevertheless, over the last 10-year period, the experience from a number of clinical trials has taught us that gene transfer is technically feasible, but that the gene delivery vehicles, or vectors, for the transfer of genetic material are still suboptimal and that treatment may have severe side effects. This review will provide examples of different genetic disorders for which gene therapy is an option and has been attempted. It will also briefly discuss the existing vector systems and mention their advantages and drawbacks.