Authors give a detailed overview on aspects of aggressive behaviour in childhood and adolescence especially on the basis of the literature of the last two decades, then. the measurement opportunities of aggression is discussed. The Children's Aggression Scale- parent version (Halperin et al 2002) rated by parents is presented and Hungarian validity data are published. In the second part of the publication, authors focus on the viewpoints of differences between aggressiveness of IQ deficit people and those of having normal intelligence, preliminary experiences are reported about the behavioural dimensions of intellectually disabled (ID) patients rated by the Behaviour Problem Inventory (BPI, Rojahn et al, 2001) suitable for measuring frequency and severity of behavioural qualities of both ID adolescents and adults.