Autism spectrum disorders [ASD] are complex neurobehavioraL disorders defined by social and communication deficits and repetitive and stereotyped behaviors. The current estimated prevalence of ASD is approximately 1:100, which reflects a 15-fold increase from studies published a half-century ago. ASD is a highly heritable disorder, however, the exact cause of ASD is still unknown. ASD is associated with altered functional and structural connectivity patterns in the frontal and temporo-limbic brain regions that occur early in life. It is now believed that environmental factors may modulate phenotypical expression of ASD that are associated with the genetic predisposition. Several possible risk factors for ASD were investigated and included advanced parental age, birth complications, prematurity, Low birth weight and assisted conception. Numerous epidemioLogical reports have failed to confirm any association between immunizations and MMR specifically or thimerosaL exposure and risk for ASD. The diagnosis of ASD can be reLiably made in the second year of Life and appears to be relatively stable over time. However, diagnosis of very young children can be quite complex due to their clinical heterogeneity and varying patterns of onset that can differ from the typical autism symptoms of an older child. It is further challenging to distinguish between developmental and/or speech delay and ASD at this early age. Standardized tests for ASD diagnosis, developmental level and adaptive skiLls have been successfully used for accurate diagnosis of ASD. Research has recently focused on possible basic measures and/or biological markers that can assist with early diagnosis of ASD. Recent studies suggest that substantial gains can be achieved by intensive behavioral intervention initiated prior to 24 months, as neural plasticity is increased and chaLLenging behaviors are less prominent. Effective early intervention should begin soon after the diagnosis is made, and be individualized, intensive, and comprehensive and should include parent education, and behavioral intervention. It is highly important for pediatricians and experts in child neurology, development and child psychiatry to recognize the early signs of ASD, diagnostic tools and effective intervention methods.