In the course of the German Collaborative PKU Study, the results of the Personality Questionnaire for Children (PFK 9–14) of 58 10-y-old patients treated early for phenylkctonuria were analyzed. The main message of our data is that patients with phenylketonuria who were treated early and strictly did not show a higher risk for severe emotional and behavioral maladjustment compared with healthy controls at the age of 10 y. The patients were characterized only by “less masculinity of attitudes.” Because no significant correlations were observed between the quality of dietary control and the results of the questionnaire, the noticed personality characteristic of the patients could be interpreted as a psychosocial consequence of the chronic disease.