We identified the frequency and assessed the validity of marketing claims made by American chiropractors, naturopaths, homeopaths, acupuncturists, and integrative medicine practitioners relating to the diagnosis and treatment of celiac disease and nonceliac gluten sensitivity (NCGS), both of which have increased in prevalence in recent years.We performed a cross-sectional study analyzing websites of practitioners from 10 cities in the United States and analyzed the websites for any mention of celiac or NCGS as well as specific claims of ability to diagnose, ability to treat, and treatment efficacy. We classified treatments promoted as true, false, or unproven, as assessed independently by 2 authors.Of 500 clinics identified, 178 (35.6%) made a claim regarding celiac disease, NCGS, or a gluten-free diet. Naturopath clinic websites have the highest rates of advertising at least one of diagnosis, treatment, or efficacy for celiac disease (40%), followed by integrative medicine clinics (36%), homeopaths (20%), acupuncturists (14%), and chiropractors (12%). Integrative medicine clinics have the highest rates of advertising at least one of diagnosis, treatment, or efficacy for NCGS (45%), followed by naturopaths (37%), homeopaths (14%), chiropractors (14%), and acupuncturists (10%). A geographic analysis yielded no significant variation in marketing rates among clinics from different cities. Of 232 marketing claims made by these complementary and alternative medicine (CAM) clinic websites, 138 (59.5%) were either false or unproven.A significant number of CAM clinics advertise diagnostic techniques or treatments for celiac disease or NCGS. Many claims are either false or unproven, thus warranting a need for increased regulation of CAM advertising to protect the public.