CMS 855I --Medicare Enrollment Application for Physicians and Non-Physician Practitioners http://www.cms.gov/Medicare/CMS-Forms/CMS-Forms/Downloads/cms855i.pdf Form 855I is completed by the following Physicians and Non-physician Practitioners: Anesthesiology Assistant Mass immunization roster biller Psychologist, Clinical Audiologist Nurse practitioner Psychologist billing independently Certified nurse midwife Occupational therapist in private practice Certified registered nurse anesthetist Registered Dietitian or Nutrition Professional Physical therapist in private practice Clinical nurse specialist Speech Language Pathologist Clinical social worker Physician assistant