347 patients with idiopathic respiratory distress syndrome, born 1971 to 1976, were included into a prospective follow-up study. 71 patients (20%) died in the neonatal period, 197 out of 276 survivors (71%) had a complete follow-up for the first year of life, 112 survivors have so far been investigated up to the age of four years. According to neurological findings the patients were classified as normal, doubtful (age 6-12 months) or minimal brain dysfunction (4 years), mild cerebral paresis (CP), or severe cerebral damage, respectively. At the age of one year 3 patients (1.5%) had severe cerebral damage, 14 (7%) showed mild CP and another 56 (28%) had doubtful findings. Very low birth weight of very short period of gestation increased the risk for abnormal neurological findings only slightly. The need for mechanical ventilation, especially for more than 14 days, increases the risk for CP. Serious complications during the neonatal period, particularly implicating cerebral stress, significantly reduces medium-term prognosis. Perinatal asphyxia, neonatal acidosis, hypoxia or hypercapnia did not correlate with impaired cerebral prognosis. Preliminary findings at the age of four years demonstrate good correlation with neurological findings obtained at the age of 12 months. One patient initially classified as normal (2%) and 5 doubtful babies (15%) had developed mild CP. Another initially doubtful baby had severe cerebral damage at the age of four years. 62 out of 78 children tested (79%) showed normal intelligence, 14 (18%) had an IQ of 70--90, and 2 (3%) less than 70.