1. Peer review is the primary method by which journals evaluate the quality and importance of scientific papers. To help editors find suitable reviewers, many journals allow or require authors to suggest names of preferred and nonpreferred reviewers. Though authors should know best who is qualified to review their papers, they also have a strong incentive to suggest reviewers that they expect to review their paper positively. 2. In this study, we examine the reviewers that are suggested as preferred and nonpreferred by authors, the use of these author suggestions by editors, and the influence of author suggestions on the peer review process and outcomes at the journal Functional Ecology. In particular, we examined how gender of the participants (author, editor and reviewer) influences the role of preferred reviewers in the peer review process. 3. Even when not required by the journal, most authors suggest preferred reviewers, but few suggest nonpreferred reviewers. Most author-preferred reviewers are male, but the proportion of women among author suggestions increased over the 11 years, from a low of 15% in 2004 to a high of 25% in 2014. 4. Male and female authors did not differ in how likely they were to suggest preferred reviewers, but the proportion of women among author suggestions was higher for female authors (~28%, averaged across years) than for male authors (~21%). Women that were suggested as author-preferred reviewers were more likely to be selected by editors than were men suggested by authors. 5. There was no evidence that editor gender, seniority or length of service as an editor for Functional Ecology affected the probability that they used author suggestions. Of reviewers invited to review, those that were author-suggested were more likely to respond to the editors' review invitations but were not more likely to agree to review. 6. Most strikingly, author-preferred reviewers rated papers more positively than did editorselected reviewers, and papers reviewed by author-preferred reviewers were much more likely to be invited for revision than were papers reviewed by editor-selected reviewers. This difference was not influenced by the gender of the participants in the process. 7. Suggesting preferred reviewers benefits authors because preferred reviewers rate papers significantly more positively than do editor-selected reviewers, improving the chances that a paper will be published. Journals and journal editors should recognize that preferred reviewers rate manuscripts differently than do editor-selected reviewers, and be aware that this difference can have large effects on editor decisions.