In this issue of the Journal, Perlis et al. report on the most comprehensive attempt to find genetic predictors of suicidal behavior (5). They tested nearly 2 million genetic variants for association with a history of suicide attempt among 5,815 individuals with bipolar disorder and 2,922 individuals with major depression. Several aspects of this study merit discussion before we turn to the results and their implications. First, Perlis et al. focused on attempted rather than completed suicide. This is a choice of convenience, since it is easier to assemble large, representative samples of suicide attempters than of completed suicides. It is reasonable to assume that genetic determinants of attempted and completed suicide overlap, since attempted suicide in a relative increases the risk of completed suicide in the proband and vice versa (2, 6). Second, the authors explored genetic correlates of suicide within a group of subjects with mood disorders. This approach is justified, since in high-income countries suicide usually occurs in the context of mental illness and mood disorders account for the largest share. In addition, genetic predilection for suicide appears to be independent of genetic liability to mental illness, meaning that findings from individuals with mood disorders can be cautiously generalized to other populations (2, 6). Third, they explored a large number of genetic variants covering all known human genes and noncoding DNA sequences. Since our knowledge of the neurobiology of suicide is imperfect, this approach represents a substantial advance on previous studies of selected genes (4). However, Perlis et al. focused on genetic variants that are carried by at least several percent of individuals (i.e., common variants). There are even more individual differences in the genome that are carried by less than one in one hundred humans. These rare variants have not been tested in the present study.