Macrocephaly is a clinical symptom with a heterogeneous cause. Besides enlarged ventricles (hydrocephalus) it can be caused by increased brain volume, expanded extracerebral spaces, intracranial cysts, and dilated vessels. Drawing on the experience of more than 8 years using transfontanellar sonography including Doppler techniques, some typical clinical and sonographic features of several forms of macrocephaly are addressed. Besides isolated familial or sporadic megalencephaly, extracerebral fluid collections are the main explanation of macrocephaly. Subdural effusions with compression of the brain by increased intracranial pressure should be differentiated from craniocerebral disproportion without increased intracranial pressure. Subependymal and subarachnoidal cysts may cause extraodinary displacements and compression of brain structures; nevertheless, the prognosis is rather optimistic, for the brain structure itself is generally not destroyed. In some infants with complex genetic, neurocutaneous, and neurometabolic syndromes, macrocephaly is an early clinical sign. The outcome in these infants is very different and dependent on the dysfunction of the brain by the specific disease (eg, storage of neurotoxic substances, dysplasia, gliosis, vascular disturbances, or brain tumors). In infants with vascular malformations the diagnosis can be established more exactly by using Doppler techniques. I recommend some practical diagnostic procedures in cases of macrocephaly. Nevertheless, in many patients with increased head size an exact statement about the further prognosis cannot be established by one examination; therefore, a developmental evaluation in combination with regular sonographic evaluation is the most valuable method in taking care of all infants with macrocephaly.