I think medical records can only be shared if you sign for it.For instance Berkshire Medical center bought out Adams internists but Adams internists ,but we were all notified and had to sign that we were ok with Berkshire Medical having our medical records.

Hospitals and Dr's offices may shared your records but it all be given in writing and you sign.

If you read your patient paperwork from Mass Gen/Brigham&Women's hospital national triad it must show what other hospitals it shares with in writing with your signature.Check your paperwork.

I'm pretty sure your free to see Beth Israel,Tufts,Boston Medical,New England Baptist ,UMass medical Worcester or whomever without MGH/B&W ever knowing .

The Leahy Clinic in Burlington is good too.