Monosomy 1p36 is a recently delineated contiguous gene syndrome, which is now considered to be one of the most common subtelomeric microdeletion syndromes. We report four unrelated patients with subtle deletions within 1p36 confirmed by high resolution karyotyping and FISH. All exhibited severe psychomotor retardation. Microcephaly, seizures, and visual impairment occurred in three subjects. Results of a first routine karyotyping were unrevealing in three probands. The diagnosis was primarily suggested on the basis of a distinct pattern of facial anomalies in all except the first case. This report illustrates that monosomy 1p36 may be recognized clinically, at least in some patients, whereas the diagnosis is easily missed on routine karyotype.