Massachusetts Rules of Professional Conduct Rule 4.1: Truthfulness in Statements to Others
In the course of representing a client a lawyer shall not knowingly:
(a) make a false statement of material fact or law to a third person; or
(b) fail to disclose a material fact to a third person when disclosure is necessary to avoid assisting a criminal or fraudulent act by a client, unless disclosure is prohibited by Rule 1.6.
Adopted June 9, 1997, effective January 1, 1998.
 A lawyer is required to be truthful when dealing with others on a client's behalf, but generally has no affirmative duty to inform an opposing party of relevant facts. A misrepresentation can occur if the lawyer incorporates or affirms a statement of another person that the lawyer knows is false. Misrepresentations can also occur by failure to act.
Statements of Fact
 This Rule refers to statements of fact. Whether a particular statement should be regarded as one of fact can depend on the circumstances. Under generally accepted conventions in negotiation, certain types of statements ordinarily are not taken as statements of material fact. Estimates of price or value placed on the subject of a transaction and a party's intentions as to an acceptable settlement of a claim are in this category, and so is the existence of an undisclosed principal except where nondisclosure of the principal would constitute fraud.
Fraud by Client
 Paragraph (b) recognizes that substantive law may require a lawyer to disclose certain information to avoid being deemed to have assisted the client's crime or fraud. In paragraph (b) the word "assisting" refers to that level of assistance which would render a third party liable for another's crime or fraud, i.e., assistance sufficient to render one liable as an aider or abettor under criminal law or as a joint tortfeasor under principles of tort and agency law. The requirement of disclosure in this paragraph is not intended to broaden what constitutes unlawful assistance under criminal, tort or agency law, but instead is intended to ensure that these rules do not countenance behavior by a lawyer that other law marks as criminal or tortious. But see the special meaning of "assistance" in the context of a lawyer's appearance before a tribunal in Comment 2A to Rule 3.3.
Corresponding ABA Model Rule. Identical to Model Rule 4.1.
Corresponding Former Massachusetts Rule. DR 1-102, DR 7-102; see also DR 1-103.