Sarcoidosis is a systemic inflammatory disease of unknown aetiology, influenced by genetic and environmental factors. However, the loci so far identified for sarcoidosis explain only a part of its assumed heritability. To identify further susceptibility loci, we performed a genome-wide association analysis using the Affymetrix 6.0 Human GeneChip followed by validation and replication stages. After quality control, 637 cases, 1233 controls and 677 619 single-nucleotide polymorphisms (SNPs) were available for an initial screening. 99 SNPs were selected for validation in an independent study panel (1664 patients, 2932 controls). SNP rs1050045 was significantly associated with sarcoidosis (corrected p=0.0215) in the validation panel and yielded a p-value of 9.22 × 10(-8) (OR 1.24) in the meta-analysis of the screening and validation stage. A meta-analysis of three populations from Germany, the Czech Republic and Sweden confirmed this finding (p = 0.024; OR 1.14). Fine-mapping and mRNA expression studies pointed to osteosarcoma amplified 9 (OS9) as the most likely candidate for the underlying risk factor. The OS9 protein plays an important role in endoplasmic reticulum-associated protein degradation and acts during Toll-like receptor induced activation of myeloid cells. Expression analyses of OS9 mRNA provide evidence for a functional mechanism underlying the detected association signal.