Kathleen Seidel is an American researcher and weblog publisher from Peterborough, New Hampshire, best known for investigations and writing on autism. Her inquiries into the work and conduct of Mark Geier and his son David Geier regarding chelation therapy and a hormone-altering drug called Lupron, led to medical board actions in multiple states that suspended Mark Geier from medical practice, and caused David Geier to be arraigned for allegedly practising medicine without a license.