The Smith-Magenis syndrome (SMS) is a rare microdeletion dysmorphic syndrome (interstitial microdeletion of chromosome 17p11.2), which occurs sporadically. Mutations in the RAI1 gene are found in part of the patients. SMS is characterized by intellectual disability and behavioural disturbances (sleep disturbances, hyperactivity, attention deficit, self-injury behaviour), craniofacial dysmorphism and defects of other organs and systems (teeth, eyes and upper respiratory and hearing disturbances, short stature, brachydactyly, scoliosis, cardiac and genitourinary defects). There are also neurological problems (muscular hypotonia, peripheral neuropathy, epilepsy and decreased sensitivity to pain). Many of the features that appear in the SMS may occur in other genetic syndromes, which may cause diagnostic difficulties. We report two cases of late diagnosed patients with the Smith-Magenis syndrome. Additionally, we present a review of literature and differential diagnosis. This may help in making the diagnosis and in giving optimal medical and psychological care to patients with SMS.