Autism can be considered as an early general developmental disorder, characterized by problems of social interaction, problems of verbal and non verbal communication, and behavioral or ideational stereotypes. However, within autism we observe a clinical heterogeneity of autistic disorders which suggests the possibility of autistic subtypes. Several authors hypothesize an analgesia among autistic children; this analgesia may be related to self-mutilation found among autistics. The current research had two objectives: 1) to develop and validate evaluation tools for measuring aggression directed towards the self (Yale-Paris Self-Injurious Behavior Scale: YAPA SIB) and pain reactivity (Pre-Linguistic Behavioral Pain Reactivity Scale: PLBPRS); instruments appropriate for autistics and capable of showing different behavioral sub-types; 2) to study in 80 autistic children pain reactivity, self-injurious behavior, and their relation in different observational situations. The results show that the scales of self-injurious behavior and pain reactivity have good discriminative capacity, good test-retest reliability, and good validity. The results suggest additionally that the apparent decreased pain reactivity observed in autistics does not derive from a real analgesia but from a different mode of pain expression related to difficulties with verbal communication, body representation and certain cognitive disorders (learning disorders, problems representing sensations and emotions, problems establishing cause-effect relationships). Additionally, there is a significant relationship between certain self-injurious behaviors and the apparent reduced pain reactivity. Interpretations of this result are presented and the possible role of stress in autism is discussed.