Objective: To investigate authorship trends in Cochrane reviews from 1996 to 2018, and to examine if the authorship criteria from the International Committee of Medical Journal Editors (ICMJE) were met for Cochrane reviews with more than 15 authors based on the text in the section “Contributions of authors.”. Methods: The median number of authors per review was calculated, and authorship trends within each editorial group were analyzed. The section “Contributions of authors” was assessed about the first and second authorship criteria from the ICMJE for reviews with more than 15 authors. Results: A total of 7447 Cochrane reviews were studied based on data from the Cochrane Database of Systematic Reviews. The median number of authors per Cochrane review was 3 in 1996 (IQR 2.5-3, range 2-3), 4 in 2007 (IQR 3-5, range 1-13), and 5 in 2018 (IQR 4-7, range 2-22). Within each editorial group, the total number of authors either increased (26/55, 47%) or was unchanged (29/55, 53%). Based on the text in “Contributions of authors,” 59% (16/27) of the reviews with more than 15 authors had authors that did not fulfil the ICMJE authorship criteria. However, the text in “Contributions of authors” was often difficult to interpret. Conclusions: The number of authors per Cochrane review gradually increased from 1996 to 2018. The ICMJE authorship criteria were probably not met by all authors in more than half of the reviews with more than 15 authors.