1) Background: The Aicardi-Goutières syndrome (AGS) is a rare congenital disease which courses with severe psychomotor delay in neurodevelopment. We studied a 3-years and 4-months old child with very important growth and weight affectation, microcephaly and loss of his developmental skills from 16-months of age, in which previous metabolic and genetic studies discarded any abnormality. Therefore diagnosis was cerebral palsy of unknown etiology. He presented spastic paraparesia, poor fine motricity, cognitive impairment and absence of oral communication. One year after discharge, a de novo mutation was detected in a single nucleotide in the gene IFIH1: c.2317G>C, being then diagnosed of AGS. 2) Methods: Blood analysis showed very low IGF-1 and slightly elevated liver transaminases. Treatment consisted in GH (0.04 mg/kg/day), melatonin (20 mg/day, and after 3-months 50 mg/day), and daily intense neurorehabilitation (5 days/week). Tests for evaluating childhood developmental milestones (GMFM-88, BDIST and the WeeFim test) were carried out every 3-months. 3) Results: The equivalent age at admission (10-months) increased to 24-months at discharge. There were clear improvements in spasticity, fine motor function, swallowing, cognition and autonomy as well as in communication, growth and weight. 4) Conclusion: Most likely melatonin blocked or decreased the interferon signature, allowing GH and neurorehabiltation to act on neurodevelopment.