Aims: The Schubert-Bornschein type of complete congenital stationary night blindness (CSNB) is a genetically heterogeneous retinal disorder. It is characterized by a non-progressive disease course, often associated with high myopia and nystagmus. So far mutations in two genes, NYX (nyctalopin) and GRM6 (metabotropic glutamate receptor 6) have been associated with this form of CSNB. The purpose of this study was to identify the genetic defect in affected male patients from Flemish families with complete CSNB. Methods: Probands with CSNB from 3 large Flemish families underwent ophthalmologic examination. DNA was extracted from peripheral blood and the coding region of NYX along with parts of the 5;UTR and 3;UTR and intronic regions covering the splice sites were PCR amplified and sequenced. Results: In the affected individuals of 3 Flemish families with the complete form of CSNB a novel NYX mutation, c.855delG was identified. This deletion is predicted to lead to a frameshift mutation, p.Asp286ThrfsX62 causing a premature stop codon. Conclusion: Previously, both single families with different mutations in NYX as well as different families with an identical mutation, suggestive of a founder mutation, have been described. The c.855delG deletion in NYX seems to be a common mutation associated with CSNB in the Flemish population from Belgium. Thus we suggest performing diagnostic testing for CSNB in the Flemish population initially directed towards the identification of this mutation. Subsequent screening for other mutations in NYX or GRM6 could be performed as a second step.