This chapter examines the hypothesis that second-trimester neural developmental disturbance is associated with increased presence of schizotypal personality disorder (SPD) characteristics, which in turn increases the risk for adult schizophrenia. First, it reviews the literature on schizophrenia and neurodevelopment and the literature on SPD and neurodevelopment. Second, the chapter reports on findings relevant to the hypothesis emanating from the Helsinki Influenza Project, which has studied a cohort of individuals exposed in utero to the 1957 type A2/Singapore influenza epidemic. The type A2 influenza epidemic lasted from October 8 to November 14, 1957. The index year cohort consisted of all children born in Uusimaa County, which encompasses Greater Helsinki, Finland, from November 15, 1957, to August 14, 1958, and diagnosed schizophrenic and admitted before the age of 29 years and 10 months as an inpatient to one or more of the eight psychiatric hospitals serving the county of Uusimaa.