The Stiff-Baby Syndrome is a genetic startle disorder, presenting soon after birth and characterized by an exaggerated persistent startle response to unexpected stimuli and generalized muscular rigidity that decreases during sleep. Hyperekplexia is often mistakenly diagnosed as spastic quadriparesis or epilepsy, therefore it should be promptly identified during the neonatal period. Its treatment with benzodiazepines alleviates the debilitating symptoms, may prevent life-threatening events and enables better feeding and handling. The disorder is mainly due to hereditary mutations of the inhibitory postsynaptic neurotransmitter receptor (glycine receptor chloride channel), but in few cases the Stiff-Baby Syndrome is caused by sporadic missense and nonsense mutations. The diagnosis of such a relatively benign disorder with a favourable developmental outcome can avoid unjustified extensive investigations or unnecessary treatments. The article reports the case of a 3-month-old baby affected by a sporadic form of Stiff-Baby Syndrome.