Cleft lip with or without cleft palate (CL/P) is one of the most common birth defects, but its etiology is largely unknown. It is very likely that both genetic and environmental factors contribute to this malformation. Mutations in the gene for interferon regulatory factor 6 (IRF6) have been shown to be the cause of Van der Woude syndrome, a dominant disorder that has CL/P as a common feature. Recently, it has been reported that genetic polymorphisms at the IRF6 locus are associated with nonsyndromic CL/P, with stronger association in Asian and South American populations. We investigated four markers spanning the IRF6 locus, using the transmission/disequilibrium test. A sample of 219 Italian triads of patients and their parents were enrolled in the study. Strong evidence of linkage disequilibrium was found between markers and disease in both single-allele (P=.002 at marker rs2235375) and haplotype (P=.0005) analyses. These findings confirm the contribution of IRF6 in the etiology of nonsyndromic CL/P and strongly support its involvement in populations of European ancestry.