PURPOSE. To identify the genetic cause of central areolar choroidal dystrophy (CACD) in a large Northern Irish family. METHODS. We previously reported linkage of the locus for CACD in this family to an interval of approximately 5 cM on chromosome 17p13 flanked by polymorphic markers D17S1810 and CHLC GATA7B03. We undertook sequence capture, massively parallel sequencing and computational alignment, base-calling and annotation to identify a causative mutation. Conventional sequencing was used to confirm the results. RESULTS. Deep sequencing identified a single-base substitution in guanylate cyclase 2D, membrane (retina-specific) gene (GUCY2D). The novel mutation segregated with the disease phenotype and resulted in substitution of valine by alanine at position 933, within the catalytic domain of the protein. It altered a motif that is strongly conserved in a large number of distantly related proteins across several species and was predicted to have a damaging effect on protein activity. CONCLUSIONS. Mutations in GUCY2D have previously been associated with dominant cone-rod dystrophies (CORD6) and recessive forms of Leber's congenital amaurosis. This is the first report of a GUCY2D mutation causing CACD and adds to our understanding of genotype-phenotype correlation in this heterogeneous group of choroidoretinal dystrophies. (Invest Ophthalmol Vis Sci. 2012; 53:4748-4753) DOI: 10.1167/iovs.12-10061