The prevalence of pervasive developmental disorder [i.e. broadly defined autism] in thimerosal free birth cohorts was significantly higher than that in thimerosal exposed cohorts (82.7 of 10 000 vs 59.5 of 10 000). . . . In fact, it was remarkable that the PDD rates were at their highest value in birth cohorts that were thimerosal free, providing a clear and convincing message on the lack of an association. . . . the rate of exposure varied from nil to very high levels of vaccine-derived ethylmercury, allowing us to test for effects along the full range of exposure and to detect possible threshold effects as well. All of the results were negative.
Rising rates of autism appear most strongly linked to improved diagnosis of the condition.
Hat Tip to Skeptico who provides extensive quotations and additional analysis.