Recurrent microdeletions and microduplications of a 600-kb genomic region of chromosome 16p11.2 have been implicated in childhood-onset developmental disorders. We report the association of 16p11.2 microduplications with schizophrenia in two large cohorts. The microduplication was detected in 12/1,906 (0.63%) cases and 1/3,971 (0.03%) controls (P = 1.2 x 10(-5), OR = 25.8) from the initial cohort, and in 9/2,645 (0.34%) cases and 1/2,420 (0.04%) controls (P = 0.022, OR = 8.3) of the replication cohort. The 16p11.2 microduplication was associated with a 14.5-fold increased risk of schizophrenia (95% CI (3.3, 62)) in the combined sample. A meta-analysis of datasets for multiple psychiatric disorders showed a significant association of the microduplication with schizophrenia (P = 4.8 x 10(-7)), bipolar disorder (P = 0.017) and autism (P = 1.9 x 10(-7)). In contrast, the reciprocal microdeletion was associated only with autism and developmental disorders (P = 2.3 x 10(-13)). Head circumference was larger in patients with the microdeletion than in patients with the microduplication (P = 0.0007). ; PUBLISHED ; Funding for this study was provided by grants from Ted and Vada Stanley, the Simons Foundation, grants from NARSAD to FJM, TGS, DLL, MCK and TW, and grants from the Essel Foundation and the Sidney R. Baer, Jr. Foundation to DLL and from the Margaret Price Investigatorship to JBP and VLW. This work was supported by grants from the National Institutes of Health Intramural Research Program, National Institutes of Health, including NIMH grant MH076431 to JS, which reflects co-funding from Autism Speaks, and the Southwestern Autism Research and Resource Center, as well as NIH grants to JS (HF004222), MCK, TW, and JMC (MH083989), DLL and NRM (MH071523; MH31340), JMC (RR000037), PFS (MH074027 and MH077139), JSS (MH061009), LED (MH44245), THS (GM081519) and CKD (MH081810; DE016442; HD04147). Funding for GK, NC, MJO and MCO was provided by the Medical Research Council, UK, and the Wellcome Trust. The CATIE project was funded by NIMH contract N01 MH90001. Genotyping of the Molecular Genetics of Schizophrenia study (PI Pablo Gejman) was funded by the Genetic Association Information Network (GAIN) of the Foundation for the US National Institutes of Health. Genotype data were obtained from dbGaP (http://www.ncbi.nlm.nih.gov/dbgap, accession number phs000021.v2.p1). This study makes use of data generated by the Wellcome Trust Case Control Consortium (full list of contributors is presented in the supplementary online material). Funding for that project was provided by the Wellcome Trust under award 076113. Microarray data and clinical information were provided by the Genetic Association Information Network (GAIN). Thanks to the New York Cancer Project, Peter Gregersen and Annette Lee for providing population control samples. Also, we wish to thank Drs. Pablo Gejman and Douglas Levinson for helpful discussions. Special thanks to Dr. James Watson for helpful discussions and support.