The Smith-Magenis syndrome (SMS) is characterized by congenital anomalies, mental retardation and the interstitial deletion of the 17p. 11.2 chromosome. The subjects affected by this syndrome show cranio-facial dysmorphias, brachycephalia, skeletal, ocular, cardiac, genitourinary and otolaryngological anomalies. The central nervous system is affected and this may be shown by psychomotor retardation, intellective deficit, electroencephalographic alterations (reduced/missing REM phase); the neuroradiological tests detect megacisterna magna, cerebellar hypoplasia, cortical dysplasia, ventricular asymmetry. Behavioural troubles are frequent and, among them, self-aggressive conducts (tearing out the nails). The syndrome is associated with the interstitial deletion of the 17p. 11.2 chromosome. The diagnosis can be made in the pre-natal period and a mosaic situation is possible. Even though the cases of SMS reported in the literature allow defining a characteristic phenotype, studies have been carried out to quantify the deletion of the chromosome 17 in order to identify the chromosomic tract which is responsible for the phenotypical induction. The deletion can either appear de novo or come from one of the parents. In addition, these subjects can show peripheral neuropathy, missing or reduced deep tendon reflexes and (rarely) epileptic crises. However, by reviewing the literature, no descriptions of patients affected by infant spasms are pointed out. This report refers to a new case of Smith-Magenis syndrome in a nine-month-old girl with spasms in extension.