Cohen syndrome (CS) represents a complex developmental disorder. Commonly observed features include: microcephaly, mental retardation, childhood hypotonia, motor clumsiness and non-progressive psychomotor retardation, joint hyperextensibility, ophthalmologic findings such as progressive myopia, retinochoroidal dystrophy, and pigmentary retinopathy, truncal obesity with slender hands and feet, and intermittent neutropenia. The facial gestalt, which becomes more distinct with age, is characterized by a low anterior hairline, thick hair, eyebrows, and eyelashes, high-arched or wave-shaped eyelids, prominent, beak-shaped nose, low nasal bridge, short, upturned philtrum, and open-mouthed appearance. Cohen syndrome is especially common in the Finnish population due to a founder mutation. While the phenotype is relatively homogenous in Finnish patients, the clinical spectrum is much wider in non-Finnish patients.