<p>Bipolar disorder (BD) significantly compromises overall functioning. Evidence supporting the benefits of cognitive-behavioral therapy (CBT) in BD highlights the need to explore its application in diverse clinical contexts. This single-case study implemented and analyzed a CBT intervention in a 59-year-old woman diagnosed with BD type I, conducted through individual online sessions. Both diagnosis and case formulation were essential for treatment progress. The identification of mixed features during mood episodes was particularly relevant, as it informed psychopharmacological adjustments and clarified the participant’s treatment nonadherence. Although the literature does not consistently report effective treatments for episodes with mixed features, this case highlights the ethical responsibility to integrate the best available evidence with specialized training and personal psychotherapy. The findings underscore the potential contributions of CBT to symptom reduction and treatment adherence, while reinforcing the need for more robust studies to establish its efficacy in BD, particularly during episodes characterized by mixed features.</p>