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Historically, the principle of reformatio in peius originates in Roman law, where the prohibition of worsening the situation of an appellant was already established. Over the centuries, this principle has been incorporated into various legal systems and has been the subject of jurisprudential interpretations in different jurisdictions.
In European law, this principle has also been developed in the jurisprudence of the European Court of Human Rights (ECHR). According to the ECHR, any alteration to the detriment of the appellant must be duly justified within the framework of a fair process. In Spain, the consolidation of this principle has been especially significant in the criminal law field, where it has become an essential guarantee for defendants.
Criminal Law
In criminal law, the principle of reformatio in peius prevents a court from worsening the situation of the accused when they are the only party appealing a sentence. This prohibition is particularly relevant in appeal and cassation proceedings, where judicial decisions are reviewed without the prosecution requesting any change to the detriment of the accused.
A crucial aspect in this field is the relationship between this principle and the accusatory principle, according to which a conviction or sentence increase can only be imposed if it has been requested by the prosecution. As a result, higher courts cannot modify the legal classification of the facts to increase the sentence unless the prosecution has filed an appeal in that regard.
Administrative and Civil Law
In administrative law, the principle of reformatio in peius also has significant application. For example, in sanctioning procedures, if a citizen appeals an administrative fine, the administration cannot increase the imposed penalty unless there is an explicit challenge in that direction. This guarantees legal certainty and prevents the exercise of the right to appeal from becoming a risk for the appellant.
In civil law, this principle operates with certain particularities. Although in disputes between private parties, the possibility of worsening one party's situation is generally limited by the claims made by the parties, the appellate court must respect the principle of congruence and cannot go beyond what has been requested in the appeal and opposition documents.
Supreme Court Judgment 139/2025, February 19
A recent case illustrating the application of the reformatio in peius principle is Supreme Court Judgment 139/2025, where a violation of this principle was examined in a criminal procedure.
Case Facts
The appellant, supported by the Public Prosecutor’s Office, claimed a violation of the accusatory principle and the principle of reformatio in peius. The situation arose when the appeal court, after acquitting the appellant of the offense of credit card fraud, took it upon itself to requalify the offense as fraud and increase the sentence imposed in the first instance.
Supreme Court's Reasoning
Upon reviewing the matter, the Supreme Court emphasized that:
Final Decision
The Supreme Court concluded that the appellate court had violated the appellant's fundamental rights and, consequently, annulled the requalification of the offense, restoring the penalty imposed in the first instance.
The principle of reformatio in peius is an essential guarantee in criminal proceedings and the appeals system, protecting the appellant from unjustified aggravations of their legal situation. Its application is not limited to criminal law but extends to administrative and civil law, ensuring fairness and legal certainty.
Supreme Court Judgment 139/2025 reaffirms the importance of this principle and its connection to the right to effective judicial protection, consolidating its application within Spanish law.
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