BackgroundThe impact factors of biomedical journals tend to rise over time. We sought to assess the trend in the impact factor, during the past decade, of journals published on behalf of United States (US) and European scientific societies, in four select biomedical subject categories (Biology, Cell Biology, Critical Care Medicine, and Infectious Diseases).MethodsWe identified all journals included in the above-mentioned subject categories of Thomson Reuters Journal Citation Reports® for the years 1999, 2002, 2005, and 2008. We selected those that were published on behalf of US or European scientific societies, as documented in journal websites.ResultsWe included 167 journals (35 in the subject category of Biology, 79 in Cell Biology, 27 in Critical Care Medicine, and 26 in Infectious Diseases). Between 1999 and 2008, the percentage increase in the impact factor of the European journals was higher than for the US journals (73.7±110.0% compared with 39.7±70.0%, p = 0.049). Regarding specific subject categories, the percentage change in the factor of the European journals tended to be higher than the respective US journals for Cell Biology (61.7% versus 16.3%), Critical Care Medicine (212.4% versus 65.4%), Infectious Diseases (88.3% versus 48.7%), whereas the opposite was observed for journals in Biology (41.0% versus 62.5%).ConclusionJournals published on behalf of European scientific societies, in select biomedical fields, may tend to close the “gap” in impact factor compared with those of US societies.What's Already Known About This Topic?The impact factors of biomedical journals tend to rise through years. The leading positions in productivity in biomedical research are held by developed countries, including those from North America and Western Europe.What Does This Article Add?The journals from European biomedical scientific societies tended, over the past decade, to increase their impact factor more than the respective US journals.