: Coffin-Siris syndrome (OMIM #135900) is an autosomal dominant inherited disorder, characterized by dysmorphic features, congenital anomalies, and developmental delay. We report the clinical and molecular findings in a patient with Coffin-Siris syndrome. A 3-year-and-6-month-old boy presented with developmental delay, distinctive facial features, hypertrichosis, partial agenesis of the corpus callosum, fifth digit nail hypoplasia, congenital anomalies, and growth retardation. Targeted gene panel sequencing identified a novel heterozygous frameshift mutation c.2147_2148insAC in ARID1B which was predicted as a premature stop codon p. (Gln717Argfs*29). This is the second report of Coffin-Siris syndrome in Korea. Targeted gene panel sequencing can be used as an effective tool for the diagnosis of rare complex syndromes such as Coffin-Siris syndrome.