BACKGROUND We report a case of type I spinal muscular atrophy (SMA), also known as Werdnig-Hoffmann disease. METHODS This was a descriptive case report. The patient was in the pediatric intensive care unit of a medical center. METHODS The patient was a 5 1/2 month-old male admitted to the emergency room from another hospital with a diagnosis of pneumonia with right apical atelectasis and with poor clinical evolution. The patient showed symptoms of acute respiratory failure and also generalized muscular weakness. Auscultation showed disseminated crackles, ronchi and hypotonic limbs. In view of his respiratory condition he was admitted to the Pediatric Intensive Care Unit and intubated. Chest X-ray showed a narrow chest with an apical infiltration and a left parahilar atelectasis. During the first days in the ICU, successful extubation was not possible because the patient showed hypoxemia and bradycardia. SMA was suspected because of the general muscular weakness; therefore, biopsy and neurophysiology studies were performed, demonstrating an axonal motor polyneuropathy with tongue fasciculations and signs of chronic denervation. The Pathology Service reported neurogenic fascicular atrophy and genetic analysis supported the diagnosis by blood test sampling, revealing a homozygous state for a deletion on exon 7 of the gene SMN1. Fifteen days after his admission to the hospital, the patient showed severe respiratory and heart failure to the CPR maneuvers. CONCLUSIONS Type 1 SMA is a rare entity with few cases reported in the literature, but it is important for the pediatrician to be familiar with this disease because of its severe implications.