Self-citation patterns of 1,104 journals indexed in the 2018 edition of the Journal Citation Reports were examined to assess the possibility of underlying rank manipulations. The journals included in this study were all found to have a self-citation rate of more than 25%. Our research shows that by excluding self-citation rates, the rank of journals with a high impact factor are not affected; however, for other journals, the removal of even a single self-citation can cause significant rank changes. Self-citation patterns are typical for local language journals as well as journals from upper-middle-income European countries. Impact factors used in research performance evaluations should be used more carefully, particularly when variables such as journal size, publication language, publisher country, and subject area correlate with self-citation rates.