Background/Objectives: Brentuximab vedotin (BV) has been shown to be effective in the treatment of classical Hodgkin’s lymphoma (cHL), systemic anaplastic large cell lymphoma (sALCL), and CD30-positive cutaneous T-cell lymphoma (CTCL). This study aimed to evaluate the effectiveness and safety of BV retreatment in patients with relapsed/refractory cHL, sALCL, and CD30-positive CTCL. Methods: This multicenter, non-interventional, retrospective medical chart review study analyzed medical records from 43 patients retreated with BV in Spain. Patients were included if they had relapsed or refractory cHL, sALCL, or CD30-positive CTCL and were previously treated with BV. Demographic characteristics, disease stage, response to treatment, survival outcomes, and adverse events were analyzed. Results: The study population included 16 patients with cHL, 13 with sALCL, and 14 with CTCL. The majority were male (58.1%) with a mean age of 46.2 years and baseline ECOG scores of 0–1. Among cHL and sALCL patients, disease stage, according to the Ann Arbor classification, ranged from I to IVB, while in CTCL, EORTC clinical stages ranged from IA to IVB. The overall response rate to BV retreatment was 76.7%, with the highest response observed in sALCL (92.3%). Complete remission was achieved in 60.5% of patients. Median progression-free survival was 25.4 months, and overall survival reached 50 months. Treatment failure occurred in 37.2% of patients. BV was generally well tolerated, with peripheral neuropathy being the most frequently reported adverse event. Conclusions: The BELIEVE study is the largest study to date demonstrating that retreatment with BV is an effective and well-tolerated option for patients with relapsed or refractory CD30-positive malignancies.