By cranial ultrasound extracerebral fluid collections with a thickness of more than 5 mm were diagnosed in 101 infants under 1 year of age (jan. 84-dec. 85). Well-known etiologic factors were found in many cases (subdural hygroma, bacterial meningitis, shunt-dysfunction, congenital malformations, ACTH-therapy). In 38 children with normal clinical and neurological aspect no definite cause could be detected. In case of normal head circumference we consider this state as a variation of the norm. In case of macrocephalus (greater than 97th percentile) we propose the terminus "cranio-cerebral dysproportion". Possible etiologies, diagnostic procedures and differential diagnosis are discussed. The knowledge of this benign condition is important to prevent children from unnecessary diagnostic and therapeutic procedures.