There is a common phenomenon seen in autism- which is regression in development. After a particular age child loses his/her abilities rapidly. This autism is considered as autism developed in toddlerhood. Parents of children, who showed regression says that the child used to say words, used to maintain eye contact, were responding to name call and suddenly stopped this after a particular age, followed by development of unusual stereotypic movements. Some research studies considering this as an onset of autism rather than regression. There are two studies which demonstrate that children who show regression also showed some subtle changes in skills before the regression. Children mainly show regression in language skills, social skills or skills other than language and social. The causes of regression are unknown. But knowing the onset of regression and noticing the changes in skills will be helpful in early intervention. Studies revealed that regression occurs within second and third years of life mostly around 20 months of age. It is important to study both the genetic and environmental factors which may leads to autism including regression.