The literal translation "mutual dissent" or "mutual disagreement" does not express what is meant by "acuerdo de mutuo disenso" in Spanish, which is a mutual agreement of the parties to discharge or annul contractual (or other) obligations. (The obligations in question will depend on the rest of the context of your text.) In English the Latin term "dissensus" is sometimes used to express this, and is defined in Black's Law Dictionary (8th ed., 2004) as "a mutually agreed annulment of a contractual obligation; an undoing of the consensus that created the obligation."

Definition of "mutuo disenso" from Diccionario de Derecho Bosch (Barcelona, 1995):

MUTUO DISENSO-También denominado contrario consensus o desistimiento mutuo, es el negocio extintivo de una relación contractual existente. Si el contrato es la situación en que las partes se encuentran imposibilitadas de desobligarse a no ser mediante el cumplimiento, cabe no obstante que celebren un nuevo contrato de signo inverso para cancelar el primero. Puede decirse que se trata también de una remisión o condonación recíproca de las obligaciones que asumieron en el contrato, que ahora extinguen por mutuo acuerdo.







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Note added at 2 hrs (2006-10-02 20:17:46 GMT)
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"Agreed discharge of contract:
In some cases the parties will simply agree to terminate a contract, so that one or both parties are released from their obligations. A distinction is generally made between bilateral discharge in which both parties receive a benefit from the discharge, and unilateral where the change is made for the benefit of one party only. In general, an agreed discharge will be binding if it contains the same ingredients that made the contract binding when it was formed..."

Source: Catherine Elliott and Frances Quinn. "Contract Law" Longman, 3rd. ed., 2001. p. 234.

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Note added at 3 hrs (2006-10-02 20:41:20 GMT)
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"Disenso" in this context does not mean "dissent" and "disenso mutuo" must be considered together as a separate expression as it is in the Diccionario de la Real Academia's definition. The DRAE defines "disenso mutuo" is as follows:

disenso.
Del lat. dissensus.
1. m. disentimiento.

mutuo disenso.
1. Der. Conformidad de las partes en disolver o dejar sin efecto el contrato u obligación entre ellas existente.

A translation of the DRAE definition shown above renders the correct English translation of "disenso mutuo": "agreement of the parties to terminate or render without (legal) effect the contract or obligation existing between them" (or whatever appropriate wording you may choose!) Thus, I believe it is clear that the expression "disenso mutuo" does not refer to "mutual dissent" or "mutual disagreement" between the parties, but rather their mutual agreement to desist from their existing contractual obligations.

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Note added at 3 hrs (2006-10-02 21:08:41 GMT)
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"mutuo disenso" is translated as "mutual termination of a contract or other act" in Cabanellas and Hoague's "Butterworth's Spanish-English Legal Dictionary", Austin, Texas: Butterworth Legal Publishers, 1991, p. 417.

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Note added at 3 hrs (2006-10-02 21:21:14 GMT)
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"acuerdo de mutuo disenso" = Mutual Termination Agreement

Examples:

Transmeta Corporation (“Transmeta” or the “Company”) entered into a Mutual Termination Agreement, effective February 6, 2006, with Culture.com Technology Limited and Culturecom Holdings Limited. Under the terms of the Mutual Termination Agreement, the parties mutually agreed to terminate two related asset purchase and license agreements.
http://investor.transmeta.com/EdgarDetail.cfm?CIK=1001193&FI...

A copy of the Mutual Termination Agreement is attached as Exhibit 10.1 hereto and is ... 10.1 Mutual Termination Agreement between and among ADC ...
biz.yahoo.com/e/060810/adct8-k.html

The mutual termination agreement settles all matters between the two companies. NPS will pay a termination fee to Enzon in the form of 1.5 million shares of ...
www.npsp.com/news/releasetxt.php?ReqId=419197

The company has signed a Mutual Termination Agreement with Technology Partnership Canada (TPC), which relieves NPS of any potential obligations related to ...
www.npsp.com/news/releasetxt.php?ReqId=493674

According to the terms of the Mutual Termination Agreement, the business (ie, lessor/lessee) relationship between the parties terminated effective November ...
www.court.state.nd.us/court/opinions/20030017.htm

... entered into a mutual termination agreement with INDUS Acquisition Company that terminates the merger agreement relating to the proposed transaction in ...
www.findarticles.com/p/articles/mi_m0EIN/is_2001_Oct_4/ai_7...