Authorship in biomedical publications establishes accountability, responsibility, and credit. Misappropriation of authorship undermines the integrity of the authorship system, but accurate data on its prevalence are limited. To determine the prevalence of articles with honorary authors (named authors who have not met authorship criteria) and ghost authors (individuals not named as authors but who contributed substantially to the work) in peer-reviewed medical journals and to identify journal characteristics and article types associated with such authorship misappropriation. Mailed, self-administered, confidential survey. A total of 809 corresponding authors (1179 surveyed, 69% response rate) of articles published in 1996 in 3 peer-reviewed, large-circulation general medical journals (Annals of Internal Medicine, JAMA, and The New England Journal of Medicine) and 3 peer-reviewed, smaller-circulation journals that publish supplements (American Journal of Cardiology, American Journal of Medicine, and American Journal of Obstetrics and Gynecology). Prevalence of articles with honorary authors and ghost authors, as reported by corresponding authors. Of the 809 articles, 492 were original research reports, 240 were reviews and articles not reporting original data, and 77 were editorials. A total of 156 articles (1 9%) had evidence of honorary authors (range, 11%-25% among journals); 93 articles (11%) had evidence of ghost authors (range, 7%-16% among journals); and 13 articles (2%) had evidence of both. The prevalence of articles with honorary authors was greater among review articles than research articles (odds ratio [OR], 1.8; 95% confidence interval [CI], 1.2-2.6) but did not differ significantly between large-circulation and smaller-circulation journals (OR, 1.4; 95% CI, 0.96-2.03). Compared with similar-type articles in large-circulation journals, articles with ghost authors in smaller-circulation journals were more likely to be reviews (OR, 4.2; 95% CI, 1.5-13.5) and less likely to be research articles (OR, 0.49; 95% CI, 0.27-0.88). A substantial proportion of articles in peer-reviewed medical journals demonstrate evidence of honorary authors or ghost authors.