This study aims to determine the readability and trustworthiness of English and Spanish hypo- and hyperthyroid-related online information. Google searches were conducted for four search terms: hypothyroidism, Hashimoto's Disease, hyperthyroidism, and Graves' Disease. For each search term, the first 10 websites were analyzed with a total of 40 websites analyzed. Readability formulas were used to determine English and Spanish readability. Trustworthiness was determined using HONcode status, JAMA Benchmark Criteria, and NLM Trustworthy Score. Overall readability largely exceeded recommended grade levels. Only 1 website (2.5%) presented information below the eighth-grade reading level based on overall Readability Consensus score, while 31 websites (77.5%) exceeded this threshold for all measures. The mean (SD) English readability grade level was 9.6 (3.44); the mean (SD) Spanish grade was 8.5 (4.58). No significant relationships were found between the JAMA Benchmark Criteria, NLM Trustworthy Score, HONcode status, and readability. 67.5% of websites analyzed (n = 27) were certified with the Health on the Net Foundation's code of conduct. Websites about common thyroid-related conditions have overall poor readability. The availability of resources for Spanish-speaking patients is also poor. Steps should be taken to ensure that online health-related materials are comprehensible. Physicians should recognize that patients may have few trustworthy and easy-to-understand sources to access information. The readability and trustworthiness of sources should be considered when providing patients suggested sources for further reading. It may be particularly helpful for physicians to utilize websites with favorable readability scores such as the American Thyroid Association website.