We report one of the youngest and most intensively studied cases of Landau-Kleffner syndrome, with a follow-up of 5 years. The boy developed normally until the age of 18 months when he had two attacks, possibly epileptic. Electroencephalogram (EEG) was normal. Over the next 5 months he lost his six to ten words, did not engage with other children and became mute. When he was 34 months old a child-psychiatrist suggested a diagnosis of pervasive developmental disorder or developmental dysphasia. An EEG 3 months later showed abnormalities typical of Landau-Kleffner syndrome. His non-verbal abilities were normal as well as his neurological examination and brain magnetic resonance imaging (MRI). A trial of clobazam and vigabatrin was unsuccessful. When he was 4 years and 9 months old he was treated with corticosteroids and within 3 months his vocabulary increased from the standard for 1 1/2 years of age to that for 2 1/2 years of age. His language abilities continued to improve slowly until a stagnation period at the age of 6 years and 9 months. A second course of corticosteroids improved his comprehension and vocabulary to an almost normal level, and his EEG normalized. A total of 11 EEGs were obtained; all included sleep, but continuous spike and wave during slow sleep was never documented. This report illustrates that Landau-Kleffner syndrome should be considered as an alternative diagnosis in children diagnosed with developmental dysphasia. An EEG including sleep should be considered, and in the presence of abnormalities a trial of anti-epileptic drugs or corticosteroids should be undertaken.