Since psychiatric disorders have genetic architectures dominated by common variants of small effects, successful elucidation in psychiatric genetics necessitates large sample sizes. Collaboration and unconventional ascertainment methods are required to fulfill this need. Electronic health records have been increasingly seen as holding great potential for research, although they often pose substantial technical, legal and ethical challenges. Universal health care and national-scale registers with comprehensive medical, developmental, demographic, and geographic information make the Nordic countries ideal for psychiatric genetic epidemiology. The Genomic Aggregation Project in Sweden is gathering genetic data from subjects with and without complex genetic diseases in a single location for standardized processing and use in a wide variety of scientific investigations. Thirty groups with >160 K genotyped samples have joined GAPS. Although GAPS is general across medicine, many psychiatric disorders are represented within GAPS, and initial studies will focus on major depressive disorder. Through in-depth genetic investigations, the genes and pathways that will be identified can be leveraged for predictive and drug-development purposes. Sweden offers exceptional possibilities for psychiatric genetics, and GAPS aims to harness the wealth of available information for research to improve human health.