This contribution is based on observations made in the course of the psycho-analytic treatment of thirty-six adolescents, 24 boys and 12 girls. These are pardy cases I have treated and supervised myself; but to a greater extent relate to material brought together over the past three years by many colleagues and students co-operating in the study of adolescents in treatment at the Hampstead Child Therapy Clinic. The study includes young people between puberty and late adolescence with neurotic or borderline psychotic disturbances. Cases are not included which presented a clear picture of delinquent personalities from the outset, though this does not mean that in the course of treatment such features have not appeared. The appearance of impulsive and delinquent features in clinical pictures where we would not expect them in other age groups belongs to the typical experiences and problems of treatment during this phase.