Ataxia-telangiectasia (A-T) is a rare autosomal recessive neurodegenerative disorder. It is characterized by early-onset, progressive cerebellar ataxia, oculomotor apraxia, choreoathetosis, conjunctival telangiectasias, immunodeficiency, and an increased risk of malignancy. Although A-T is known to be the most common cause of progressive cerebellar ataxia in childhood, there have been no confirmed cases in Korea. We report the clinical and genetic findings of Korean siblings who presented with limb and truncal ataxia, oculomotor apraxia, choreoathetosis, and telangiectasias of the eyes. Sequence analysis of the ataxia-telangiectasia mutated (ATM) gene revealed a known missense mutation (c.8546G>C; p.Arg2849Pro) and a novel intronic variant of intron 17 (c.2639-19_2639-7del13). Reverse-transcription PCR and sequencing analysis revealed that the c.2639-19_2639-7del13 variant causes a splicing aberration that potentiates skipping exon 18. Because A-T is quite rare in Korea, the diagnosis of A-T in Korean patients can be delayed. We recommend that a diagnosis of A-T should be suspected in Korean patients exhibiting the clinical features of A-T.