Gender disparity exists among authors of the oncology literature. To quantify trends in authorship by gender within a comprehensive data set of Medline-indexed oncology articles in medical journals with high impact factors. This cross-sectional study used Medline citations to examine archives of research journals from 3 disciplines in the oncology literature. Authors from all oncology-related articles with Medical Subject Headings terms assigned from 2002 to 2018 from 13 general oncology/medicine, radiation oncology, and surgical journals were included for analysis, encompassing clinical trials, observational studies (excluding case reports), reviews, systematic reviews, meta-analyses, and all other published articles. Data were analyzed between April and May 2020. Authors were assigned genders based on societal naming norms via third-party gender identification service Gender-API.com. This assignment was internally validated based on manually obtained publicly available data on the internet. Trend in female authorship over time while considering journal type, authorship position, and article type. A total of 420 526 authors from 58 368 articles were found, of which 400 945 were assigned a gender based on their name. In total, 29.5% (95% CI, 29.4%-29.6%) of authors were identified as female, rising from 25.5% (95% CI, 24.7%-26.3%) in 2002 to 31.7% (95% CI, 31.2%-32.3%) in 2018. Each subgroup of primary article type by journal type saw a rise in female authorship over the studied period. For primary articles, last authors were less likely to be women than first authors, regardless of journal type, year, and primary article type (eg, general oncology: odds ratio [OR], 0.60; 95% CI, 0.52-0.69). For general oncology articles, women were less likely to be authors of clinical trials at each authorship position than authors at that respective position for observational studies (first, second, and last authors: OR, 0.58; 95% CI, 0.49-0.67; other authors: OR, 0.84; 95% CI, 0.79-0.89). This difference was not seen for radiation oncology or surgical oncology journals. This cross-sectional study found that female authorship in oncology research literature has increased. However, there remains a dearth of female senior authors, and the overall rise in female authorship has not kept up with the rise in female oncology faculty.