The European Court of Justice (ECJ) recently issued a ruling (Ruling) holding that a PE sponsor had been correctly found jointly and severally liable for its portfolio company’s antitrust violations under E.U. competition law. Although the sponsor did not own all (or almost all) of the company’s share capital, the ECJ ruled that its voting rights supported a rebuttable presumption that it exercised decisive influence; therefore, it should be treated as a single undertaking under Articles 101 and 102 of the Treaty on the Functioning of the European Union. The Ruling confirms the real – and seemingly increasing – risk that PE sponsors may be found jointly and severally liable for their E.U. portfolio companies’ violations of E.U. antitrust laws, and that any sponsor with a nexus to the E.U. needs to be mindful of that possibility. This article summarizes the Ruling and provides insights from attorneys about the implications for PE sponsors, as well as steps that may be taken to mitigate the potential risks. See our three-part series on parental liability in the E.U.: “‘Undertakings’ and Potential Scope of Risk for PE Sponsors” (May 21, 2019); “Rebuttable Presumption of Decisive Influence and Four Misconceptions About Avoiding Liability” (Jun. 4, 2019); and “Mitigating Liability at Various Stages of Portfolio Company Ownership” (Jun. 11, 2019).