We conducted a GWAS meta-analysis of 28 OCD case–control cohorts of European ancestry, comprising 53,660 cases and 2,044,417 controls (effective sample size, ~210,000 individuals). Ascertainment of cases varied across cohorts: OCD diagnosis was determined (1) by a healthcare professional in a clinical setting (18 cohorts, n = 9,089 cases), (2) from health records or biobanks (seven cohorts, n = 9,138 cases), (3) in a clinical setting or from health records with the additional characteristic that all OCD cases were primarily collected for another psychiatric disorder (three cohorts, n = 5,266 cases) or (4) by self-reported diagnosis in a consumer-based setting (23andMe, Inc., n = 30,167 cases). Cohort details, including phenotypic assessment, quality control and individual cohort GWAS analyses, are described in Supplementary Note 2 and Supplementary Table 1. We identified 30 independent (defined in Supplementary Note 3) loci among the 1,672 SNPs that exceeded the genome-wide threshold for significance (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P < 5{\times 10}^{-8}$$\end{document}P<5×10−8; Manhattan plot in Fig. 1, regional association plots and forest plots in Supplementary Figs. 2–31 and a list
