Scientific publication is experiencing an increase in ethical breaches, among them authorship irregularities. A cross-sectional study was conducted of all the papers published in a scientific journal after their presentation at medical students' national scientific conferences in Peru in the period 2010-2014, with the purpose of identifying inconsistencies in the number of authors and their associated factors. The evaluation focused on inconsistencies in the number of authors in the paper presented at the national scientific conferences and the published version. Poisson regression analysis was used to develop crude and adjusted models to quantify the association with the possible related factors. Review of 97 papers published in scientific journals found authorship inconsistencies in 53.6% (n = 52), a figure that increased significantly when the corresponding author was the advisor (AR: 1.51, CI 95 %: 1.10‒2.08, p = 0.012) and when the study was experimental (AR: 1.54, CI 95 %: 1.13‒2.11, p = 0.006). More than half of the papers published by medical students in Peru contained authorship inconsistencies, which could suggest the occurrence of honorary and/or ghost authorship.