A Japanese boy with interstitial deletion of the long arm of chromosome 14, including band 14q31, is described. The characteristic dysmorphic facial features, such as dolichocephaly, bushy eyebrows, horizontal narrow palpebral fissures, long philtrum, etc, and mental and motor developmental delay were observed. Other characteristic clinical manifestations were anuresis and status nonepileptic myoclonia The finding of delayed myelination of the cerebral white matter was observed on magnetic resonance examination, suggesting that an unknown factor related to myelination in the central nervous system might be localized in band 14q31.