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 × 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 × 10⁻⁷), bipolar disorder (P = 0.017) and autism (P = 1.9 × 10⁻⁷). In contrast, the reciprocal microdeletion was associated only with autism and developmental disorders (P = 2.3 × 10⁻¹³). Head circumference was larger in patients with the microdeletion than in patients with the microduplication (P = 0.0007).