The recent advent of commercially available genetic tests for the diagnosis of several mental illnesses has led to intense controversy amongst the psychiatric research community. In this article the authors review these developments, and contrast these with the growing evidence from genome-wide association studies that highly heritable psychiatric conditions such as schizophrenia are due to the contributions and interaction of multiple allelic variants, each of small effect size. There is also evidence for the contribution of some highly penetrant rare de novo copy number variants, though the lack of disease specificity for these is of concern. This article outlines the prerequisites for predictive and diagnostic genetic tests, such as clinical validity and utility, and reviews the opportunity that genetic tests for mental illnesses present. As the scientific discourse on genetic tests for complex disorders is not limited to psychiatry, the authors outline current thoughts on the significance of genome-wide association studies across health, and the phenomenon of direct-to-consumer tests in medicine. The attitudes and understanding of patients, families, and clinicians about the future (currently hypothetical) scenario of psychiatric genetic tests are discussed, as is the potential for such testing to increase, rather than diminish stigma. Finally, recommendations on the future development and availability of genetic tests in psychiatry are provided.