With the advancement of ophthalmological genetics, the molecular basis for more and more eye diseases can be elucidated. Congenital fibrosis of extraocular muscle (CFEOM) is an example. It is characterised by a congenital non-progressive restrictive ophthalmoplegia and ptosis. It is an autosomal dominant disease, caused by mutations of the KIF21A gene. With positive family history and typical ophthalmological findings, mutational analysis of KIF21A gene should be performed, not only to confirming the diagnosis, but also to offer a prognosis, for genetic counselling, and the possibility of prenatal diagnosis. Here we report the first KIF21A mutation associated with CFEOM1A in Hong Kong.