Background: Before radical mastectomy with immediate latissimus dorsi flap reconstruction, single-shot paravertebral block (PVB) can be added to general anesthesia to improve analgesia. As this technique was introduced in 2014 in our centre, our aim was to retrospectively assess its clinical effects. Methods: Among 175 patients who underwent surgery over four years (40 receiving PVB), we studied the intra-operatively administered doses of opioids and vasopressors, postoperative pain as estimated by a composite score based on the intensity scores for maximum postoperative pain and the amounts of analgesic drugs, and the report of postoperative nausea/vomiting (PONV). The effect of PVB on these outcomes was tested by propensity-matched comparisons, after a propensity score based on the patient's age, body mass index, ASA and Apfel scores, was calculated. Depending on the outcomes, results are expressed as odds ratios (OR) or regression coefficients (RC), with their 95% confidence interval limits. Results: PVB reduced the doses of intraoperative opioids (OR for comparisons between the 2nd and 3rd tercile to the 1st tercile, respectively: 0.39 (0.21; 0.67) and 0.10 (0.05; 0.21)). It increased the doses of intraoperative vasopressors (CR = 1.94 (0.89; 2.93). It reduced the composite score for postoperative pain (CR = -0.80 (-1.04; -0.56), and the occurrence of PONV (OR = 0.21 (0.14; 0.37). Conclusions: Despite a higher risk of intraoperative hypotension, single-shot PVB seems to markedly improve postoperative analgesia and reduce the amounts of opioids. This could offer many clinical advantages in this type of cancer surgery.