Genome-wide significant findings for psychiatric disorders - including neurodevelopmental disorders - are sparse, and replication of these findings has only been achieved through large international collaborations (such as the Psychiatric Genomics Consortium) using very large sample sizes (with tens of thousands of cases and controls). These enormous samples are required due to phenotypic heterogeneity, polygenicity, and generally small effect sizes of individual (common) genetic variants. This has severely hampered progress in understanding the genetic etiology of psychiatric disorders. Additionally, cross-disorder genetic overlap shows that diagnostic categories for those disorders do not follow the underlying biology well. There is now substantial evidence from phenotypic studies that psychiatric and neurodevelopmental disorders represent the extreme ends of normal distributions of disorder-like traits within the general population. For some disorders, it has also been demonstrated that there is genetic overlap between the disorder and disorders-like traits. This strengthens the hypothesis that using (genome-wide) genetic association studies of disorder-like population traits for gene discovery in psychiatric/neurodevelopmental disorders could offer immense opportunities to our field, as we can greatly increase our sample sizes at relatively little cost. Additionally, such population traits can occur across different (co-morbid) psychiatric/neurodevelopmental disorders, which can provide insight into genetic and biological susceptibility factors that are common to multiple disorders. The proposed symposium aims to provide an overview of recently conducted genetic studies of psychiatric disorder-like traits in population-based samples and, linked to this, how these studies could aid gene discovery in psychiatric genetics. More specifically, we will show how using genome-wide genetic data together with the ever-increasing amount of phenotypic trait data from very large population samples can lead to the identification of novel genes and biological mechanisms for several, clinically overlapping psychiatric disorders. In the first talk, Christie Burton (the Hospital of Sick Children, Toronto, Canada) will explain how she and her colleagues have used a trait-based approach in a large population-based childhood cohort for which they collected genetic, behavioral and cognitive data from children visiting the Ontario Science Centre. She will discuss the feasibility and power of using a quantitative trait in community samples to elucidate genetic contributors to psychiatric disorders. Secondly, Joanna Martin (Karolinska Institutet, Stockholm, Sweden) will discuss recent findings on the association of polygenic risk scores for 8 psychiatric disorders with disorder-related traits in a population sample of Swedish twins. In the third talk, Lucy Riglin (Cardiff university, Cardiff, UK) will discuss her findings of association between the genetic risk for certain psychiatric disorders and (ab)normal childhood neurodevelopment, using general population samples. All three talks will highlight the potential of trait genetics for gene finding in psychiatric disorders. In the final talk, Janita Bralten (Radboud University Medical Centre, Nijmegen, the Netherlands) will give an example of a trait-based approach that was used for discovering novel genetic and biological risk factors for autism spectrum disorders (ASDs).