In a pilot study, the possible influence of the inherited electroencephalogram (EEG) pattern on aspects of psychologic maturation was investigated. The twin sample consisted of 208 pairs, 110 monozygotic (MZ) and 98 dizygotic (DZ), mostly children and adolescents. The study showed a greater similarity between MZ compared with DZ twins in an immaturity score constructed from the Baum test (Koch 1976) and in a teacher's maturity scoring of essays. For both parameters, a correlation between occipital alpha-frequency and the test criterium could be demonstrated. This correlation was in the direction expected, and it was significant statistically. This result suggests an influence of genetically determined variation of brain maturation on interindividual variability of psychologic variation. Due to shortcomings of the methods used in the study, more specific conclusions cannot be drawn; the problem needs further elucidation using modern methods.