While the degrees and licenses are equivalent, there are many distinctions between the two professions. All DOs graduate from Osteopathic Medical Schools regulated by American Osteopathic Associations's Commission on Osteopathic College Accreditation (COCA, while MDs graduate from US or International Allopathic Medical Schools.
1) The largest difference is all DOs receive basic training in Osteopathic Manipulative Medicine which includes both diagnostic and therapeutics (Osteopathic Manipulative Treatment or OMT) as well as a holistic philosophy of health and disease.
2) Beyond that, DOs tend towards primary care and a higher percentage practice in rural areas. Osteopathic medical schools often have their highest ranking in primary care. Osteopathic medical students more often spend more of their training in community hospitals while MD students more often train in large academic research centers.
3) DO medical schools are independently regulated from MD schools, and are often located in smaller cities and more rural states. However, all US medical residency programs have oversight from the Accreditation Council for Graduate Medical Education (ACGME) and participate in a common Match.
4) All DOs must pass the first two steps of COMLEX (the Comprehensive Osteopathic Medical Licensing Exam) in order to graduate and can opt to take the USMLE as well. All physicians must pass Step 3 in either series that they have passed the first two in order to become licensed.