BACKGROUND Hyperbaric 5% lidocaine has been associated with transient neurologic symptoms (TNSs) after spinal anesthesia. A prospective, masked, randomized study was conducted to compare the incidence of TNSs after spinal anesthesia with hyperbaric 5% lidocaine or 5% prilocaine to assess the utility of prilocaine as an alternative to lidocaine in patients having short surgical procedures. METHODS The number of patients to be enrolled (100 per group) was determined by power analysis (80%, P = 0.05) considering an incidence of TNSs after spinal anesthesia with lidocaine of at least 11% according to data reported in other studies. Two hundred patients scheduled for elective surgery expected to last <60 min were allocated at random to receive spinal anesthesia with hyperbaric 5% lidocaine or hyperbaric 5% prilocaine. Three to 5 days after spinal anesthesia, all patients were interviewed by an anesthesiologist who was blinded to the group assignment and details of the anesthetic and surgical technique using a standardized symptom checklist. Patients with symptoms underwent neurologic examination. RESULTS Both groups were comparable with regard to demographic data and details of the surgical and anesthetic procedures. The incidence of TNSs in both groups was low and differences were not found (4% in the lidocaine group and 1% in the prilocaine group). The mean age of patients with TNSs (58 yr) was higher than that of patients without TNSs (48 yr; P < 0.05). No relation with any of the other variables was found. CONCLUSIONS The low incidence of TNSs among lidocaine-anesthetized patients (4%) may account for the lack of significant differences between hyperbaric 5% lidocaine and 5% prilocaine and to the insufficient power of the study to exclude the possibility of a type II error.