MBBS is enough to become a Doctor...But if you want to gain further knowledge in any particular field...then you should opt for MD or MS.

Dear Suzan, technically, a MBBS degree is a pre requisite for practising Medicine in India. MD or MS is an additional qualification to pursue your subject of interest in a specific field of Medicine. If you want to be a General Physician, MBBS will do. But if you want to specialise in a specific field for example say either Eye, Nose or Throat, you need to study MS in ENT. If you are interested of more in the field of Orthopaedics, you should study MD (Surgery) Orthopaedics so on and so forth.