A case with a rare chromosomal abnormality: isochromosome 18p: Isochromosome 18p(i(18p)), is a rare chromosomal disorder that occurs once in about every 140.000 live births and affects males and females equally. Most of the cases are due to a de nova formation but in the literature familial cases were reported. Here, we report a young female with dysmorphic features as microcephaly, frontal bossing, strabismus, low-set ears, small pinched up nose, small mouth, high palate and long philtrum, presenting a small metacentric chromosome. Besides the dysmorphic features she also has gastroesophageal reflux, spasticity, strabismus and specific brain MRI findings as dilatation of the right lateral ventricle trigonum occipital horn (colpocephaly), thinning of the corpus callosum especially of the posterior part and abnormality of the white matter myelinisation at the frontal and occipital region. Particularly the MR findings are rarely reported in the literature.