To assess whether loci other than GLC3A, GLC3B, and GLC3C are linked to primary congenital glaucoma (PCG).The gene CYP1B1 at GLC3A was screened in 19 Iranian PCG probands who had been recruited mostly from among individuals of Turkish ethnicity and individuals from central and eastern Iran. The gene MYOC was screened in patients from this cohort who lacked CYP1B1 mutations and in ten patients previously shown not to carry CYP1B1 mutations. Family members of 19 probands without mutations in either of these genes were recruited for assessment of linkage to GLC3B and GLC3C by genotyping microsatellite markers. In total, 127 individuals, including 35 affected with PCG, were genotyped.Eleven (57.9%) of the newly recruited PCG patients did not carry disease-associated mutations in CYP1B1. Disease-associated MYOC mutations were not observed in any of the patients screened. Inheritance of PCG in all the families was consistent with an autosomal recessive pattern. Linkage to GLC3B and GLC3C was ruled out in nine of the families on the basis of autozygosity mapping and haplotype analysis.Observation of the absence of linkage to GLC3B and GLC3C in at least nine families without CYP1B1 mutations suggests that at least one PCG-causing locus other than GLC3A, GLC3B, and GLC3C may exist. The disease-causing gene or genes in the novel locus or loci may account for PCG in a notable fraction of Iranian patients.