Background: Ultrasound-guided pectoral nerve block type II is a recently proposed technique for postoperative analgesia after breast cancer surgery. The thoracic paravertebral block is widely used for this purpose by decades. The presented study compares the efficacy of these two techniques for postoperative analgesia. Materials and methods: Sixty adult women were undergoing unilateral radical mastectomy or quadrantectomy with axillary dissection. The patients were randomized to receive either pectoral nerve block with 30 ml ropivacaine 0.375% (Pecs group) or thoracic paravertebral block with 20 ml ropivacaine 0.5% (TPVB group). The evaluated variables included pain intensity by the numerical rating scale at 0, 2, 4, 6, 12, 18 and the 24 hours, 24-hour postoperative opioid (promedol) and nonopioid (ketoprofen) consumption and the time to first rescue analgesia. Results: There were no statistically significant differences between both groups in the pain intensity after surgery. Ten (33%) patients from Pecs group and nine (30%) patients from TPVB group did not require any analgesia within the first 24 hours (P = 0.793). The mean postoperative ketoprofen consumption was lower in Pecs group: 63.3 (± 66.87) mg vs. 90.0 (± 84.49) mg (Р = 0.283). The number of patients who required promedol was 6 (20%) vs. 8 (27%) in Pecs and TPVB groups, respectively (Р = 0.542). The time to first analgesic request was longer in Pecs group, 550 (400.0–600.0) min vs. 510 (360.0–600.0) min (Р = 0.506) in TPVB group. Conclusions: In breast cancer surgery, the pectoral nerve block type II with ropivacaine 0.375% can provide postoperative analgesia that is comparable to the single-level thoracic paravertebral block.