OBJECTIVE: To test the hypothesis that prenatal exposure to the Hong Kong flu, an influenza pandemic that haunted Europe during winter 1969 to 1970, was associated with reduced intelligence in adulthood. METHODS: Data from the Medical Birth Register of Norway were linked with register data from the National Conscript Service. The sample comprised all registered boys born alive in single birth after 37 to 43 weeks' gestation during 1967 to 1973 (n = 205,634). Intelligence test scores, recorded at military conscription, were available for 182,913 individuals. RESULTS: The mean intelligence score increased from one birth year to another, except for a downturn in 1970. The birth year 1970 was inversely associated with intelligence score (-0.03 standard deviation [SD]; p
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Comment In: Ann Neurol. 2009 Sep;66(3):266-719798639