Two years after the First World War ended there was a surge in European birth rates, including in Norway that had been a neutral country. This paper tests the hypothesis that it was in fact the Spanish influenza that caused the Norwegian baby boom rather than the close of the war. The paper uses multivariate regression analysis, while previous studies have been univariate and largely descriptive. By using regional monthly data, the independent effect of the Spanish influenza morbidity on fertility over the years 1918-1920, net of the effect of mortality, is estimated. The fact that Norway was neutral was important in counterbalancing the influence of the war on fertility and nuptiality. Furthermore, the Norwegian data utilized in the analysis are of superior quality in a European context in that registration of population data, including vital statistics, continued normally in Norway undisturbed by the war.