Objective: To refine a previously reported linkage peak for endometriosis on chromosome 10q26, and conduct follow-up analyses and a fine-mapping association study across the region to identify new candidate genes for endometriosis. Design: Case-control study. Setting: Academic research. Patient(s): Cases = 3,223 women with surgically confirmed endometriosis; controls = 1,190 women without endometriosis and 7,060 population samples. Intervention(s): Analysis of 11,984 single nucleotide polymorphisms on chromosome 10. Main Outcome Measure(s): Allele frequency differences between cases and controls. Result(s): Linkage analyses on families grouped by endometriosis symptoms (primarily subfertility) provided increased evidence for linkage (logarithm of odds score = 3.62) near a previously reported linkage peak. Three independent association signals were found at 96.59 Mb (rs11592737), 105.63 Mb (rs1253130), and 124.25 Mb (rs2250804). Analyses including only samples from linkage families supported the association at all three regions. However, only rs11592737 in the cytochrome P450 subfamily C (CYP2C19) gene was replicated in an independent sample of 2,079 cases and 7,060 population controls. Conclusion(s): The role of the CYP2C19 gene in conferring risk for endometriosis warrants further investigation. © 2011 by American Society for Reproductive Medicine.