Patients with infantile spinal muscular atrophy rarely decide to have their own children especially if there is major respiratory impairment. We studied prospectively the pregnancy course and outcome of a 34-year-old woman with spinal muscular atrophy type II who delivered a healthy boy. Pregnancy was entirely uneventful, except that for 1-2 weeks after the caesarean section, the patient was extremely weak with dyspnoea and bulbar involvement. Several weeks after delivery her motor function had returned to pre-pregnancy levels. Pulmonary function remained stable throughout pregnancy, and thereafter, at approximately 70% predicted levels for forced vital capacity and for forced expiratory volume in 1 s. Blood gases after midgestation revealed low normal PaO(2) values around 85 mmHg and concomitant hyperventilation resulting in PaCO(2) levels below 30 mmHg.