ObjectivesPatients with metastatic renal cell carcinoma (mRCC) face complex treatment decisions and frequently turn to the Internet for treatment information. The content of patient educational websites about mRCC treatment has not been evaluated. This study evaluated the accuracy, readability, and quality of websites about the treatment of mRCC. MethodsA total of 2,700 Internet queries were performed. Across 3 Internet search engines, 25 links of 36 permutations of mRCC keywords and their synonyms were screened for eligibility. Eligible websites were English-language websites containing information about mRCC treatments. Sponsored, social media, provider-facing, and news websites were excluded. Accuracy of eligible websites was evaluated in 2 domains: (1) Completeness by calculating the percentage of mRCC facts included in websites using an investigator-created checklist based on the NCI's RCC Treatment (PDQ®)–patient version, and (2) Correctness by identifying incorrect statements that were inconsistent with guidelines. Websites containing ≥60% of checklist items had a “passing” completeness score. Incorrect statements were tallied and qualitatively categorized. Readability was evaluated using the Fry and SMOG formulae, which calculate reading grade levels. Quality was evaluated using validated instruments that appraise health information quality: QUEST (scored 0–28), which focuses on online information, and DISCERN (scored 16–80), which focuses on treatment choices. ResultsThirty-nine websites were analyzed. Mean completeness score was 30% (range 0%–69%); only 2 (5%) websites had a passing score. Twelve (31%) websites had ≥1 incorrect statement, such as listing homeopathy or hormone therapy as mRCC treatment options, or including outdated statements. Mean readability levels were 11th and 12th grades for the Fry and SMOG methods, respectively. No website had a reading level lower than 9th grade. Mean QUEST score was 19 (range 9–28); authorship, complementarity, and currency items had the lowest scores. Mean DISCERN score was 56 (range 42–76), with 7 (18%) websites rated “excellent”, 22 (56%) rated “good”, and 10 (26%) rated fair. ConclusionsMany websites about mRCC treatment have incomplete, inaccurate, and unreadable information. Quality is highly variable. Efforts to improve accuracy, readability, and quality are needed to ensure that patients with mRCC can make well-informed treatment decisions and avoid harm from misinformation.