To compare unilateral spinal block produced with small doses of hyperbaric ropivacaine with that produced by 2 doses of hyperbaric levobupivacaine, we randomly allocated 91 ASA physical status I-II outpatients undergoing knee arthroscopy to receive unilateral spinal anesthesia with 7.5 mg of hyperbaric ropivacaine 0.5% (group Ropi-7.5, n = 31) or either 7.5 mg (group Levo-7.5, n = 30) or 5 mg (group Levo-5, n = 30) of hyperbaric levobupivacaine 0.5%. Spinal anesthesia was performed at the L3-4 interspace using a 25-gauge Whitacre spinal needle. The lateral decubitus position was maintained for 15 min after injection. Strictly unilateral sensory block was present in 73%, 50%, and 61% of cases in groups Ropi-7.5, Levo-7.5, and Levo-5, respectively, 30 min after injection (P = 0.40), and unilateral motor block was observed in 94%, 93%, and 83% in groups Ropi-7.5, Levo-7.5, and Levo-5, respectively (P = 0.31). One patient of group Ropi-7.5 required general anesthesia to complete surgery, and fentanyl supplementation was required in one patient of group Ropi-7.5 (3%) and one patient of group Levo-5 (3%) (P = 0.42). The median (range) time for spinal block resolution was shorter in group Ropi-7.5 (135 [126-154] min] than in group Levo-7.5 (162 [148-201] min) (P = 0.04); whereas home discharge was shorter in groups Ropi-7.5 (197 [177-218] min) and Levo-5 (197 [187-251] min) as compared with group Levo-7.5 (238 [219-277] min) (P = 0.02 and P = 0.04, respectively). We conclude that 7.5 mg of 0.5% hyperbaric ropivacaine and 5 mg of 0.5% hyperbaric levobupivacaine provide adequate spinal block for outpatient knee arthroscopy, with a faster home discharge as compared with 7.5 mg of 0.5% hyperbaric levobupivacaine.