We present a clinical study of 43 macrocephalic children with a normal rate of headgrowth. The aims of the study were an evaluation of the usual criteria of macrocephaly and the drafting of a differentiated approach to the investigation of macrocephalics. Firstly, the value of head measurement in evaluating intracranial volume was assessed. As a golden standard for the intracranial volume the volume obtained by means of a CT-scan technique was used. It appeared that only about 30% of the variance of the intracranial volume was determined by the occipito-frontal circumference (OFC). A better estimation of the intracranial volume of the macrocephalic children was obtained by means of the "Utrecht Head Measure", the product of OFC-squared and the head height. Based on length measurements taken from CT-scans, the macrocephalic children were divided into three subgroups: megalencephaly (n = 15), extraventricular obstructive hydrocephalus (n = 5) and communicating hydrocephalus (n = 23). The clinical pictures of the megalencephalic and hydrocephalic children appeared to differ substantially. The megalencephalic subgroup had less neurological symptoms and physical abnormalities and showed a higher intelligence or a more advanced development or both. On the basis of our experience and theoretical considerations guidelines were developed for the assessment of patients with macrocephaly and a normal rate of head growth with a differentiated approach for megalencephalic and hydrocephalic patients.