In Reply We thank the correspondents who have written concerning our article1 and we are pleased to respond to points they have made. Lees is incorrect in stating there was no recruitment flowchart with participants exclusion/inclusion criteria shown, for that information was detailed in a Study Design and Recruitment Figure in the body of the article. Lees mentions that there was neither an a priori hypothesis nor a predefined primary outcome given, and that is true. Our goal was to evaluate a large number of prenatal ultrasonography variables and to determine how many of these, if any, were statistically associated with later autism. It turns out that only 1 such variable was found.