The increased diagnoses of autism and developmental disorders in recent decades, together with the childhood vaccination program, has led to the hypothesis that vaccination in general, and the measles, mumps, and rubella virus live vaccine, and vaccines that contain mercury, in particular, cause autism. It has been hypothesized that intestinal infection caused by live virus vaccines change the permeability of the intestinal wall, and subsequently, the passage of peptides through the intestinal wall to the blood, and from there to the brain. It has been suggested that the accumulation of these peptides in the central nervous system causes autism. Studies that investigated this theory did not find an association between vaccine administration and between digestive system symptoms and autism. According to a second hypothesis, an organomercury compound (Thimerosal), used as a preservative in vaccines that do not include live viruses, is a cause of autism. Like the former, this hypothesis has been well researched, and refuted. Some studies have in fact found an increase in autism diagnosis among children who were vaccinated after Thimerosal was removed from the vaccine preparation. Recent studies have refuted the theory that the consecutive administration of vaccines weakens the young immune system in children, and leads to an autoimmune process that causes autism. The etiology of autism is still unknown, with research continuing from different directions. The extensive research conducted so far indicates that childhood vaccination is not a cause of the sharp increase in autism diagnoses in recent decades.