Ego defense mechanisms were studied in three groups of early adolescents: diabetic patients, non-psychotic psychiatric patients, and healthy high school students. Defenses were assessed from ratings of open-ended, in-depth interviews. High levels of denial and low levels of asceticism were found in all three groups. Comparisons between groups indicated that psychiatric patients had a distinctive profile of defense usage, in comparison to adolescents from the other two groups. An independent measure of ego development was positively correlated with the defenses of altruism, intellectualization, and suppression, while it was negatively correlated with acting out, avoidance, denial, displacement, projection, and repression. The findings of substantial differences in defense usage between the psychiatric and non-psychiatric samples, and the size and directions of the correlations with ego development level, lend support to the validity of the defense codes.