Written informed parental consent in a double blind randomized clinical trial, 66 infants (ASA I or II), undergoing inguinal hernia repair will be recruited in Tabriz Teaching Children Hospital during a 12-month period of time. We explained these two forms of regional anesthesia and their complications to the parents throughout the preoperative visits. All patients were given IV midazolam (0.03 mg/kg) before performing block.. Monitoring included pulse oximetry, electrocardiogram, and non-invasive blood pressure monitoring and precordial stethoscope. A maintenance IV 5% dextrose in was infused from the start of preoperative fasting time (4 hours prior to the operation). In group C, infants were in left lateral position with flexion of hip. A 22-gauge caudal needle was selected to perform the block. After negative aspiration test, we injected 1ml/kg of 0.25% Bupivacaine, with 20μg adrenaline 1:1000 in caudal space, then the infant was turned into supine position.Successful caudal anesthesia was defined as lack of sensation to pinch at the desired sensory level and paralysis of lower limbs after 15 minutes. In group S, an assistant seated the infant on a folded towel 10 cm above the operative table. The head was placed in neuter positional 2.5cm, 25-gauge Quincke spinal needle was inserted into L5-S1interspace. This approach was adopted to avoid potential damage to the conus medullaris terminating at L3 in infants. Subarachnoid placement was confirmed by free flow of CSF. With the needle stabilized, the local anesthetic solution i.e. 1mg/kg of 0.5% hyperbaric Bupivacaine, with 20μg adrenaline 1:1000 was rapidly injected. The patient was immediately positioned supine with a 20-30° head up tilt for two to three minutes, and then horizontally. Successful spinal anesthesia was defined as lack of sensation to pinch at the desired sensory level and paralysis of lower limbs after 2 minutes. In all patients, we recorded vital signs (systolic and diastolic blood pressure, heart rate and SpO2) before induction, after 10, 20, and 30 minutes of block, at the end of surgery, at the beginning of the recovery, 10 and 20 minutes of the recovery phase, and at the end of the recovery. We also recorded presence of apnea and need for analgesia at the post-operation period up to 24 hour. NIPS was used to assess pain score; consisting of six criteria: facial expression, cry, breathing pattern, arms and legs positions, and state of arousal. In group c 25 min after block and in group s just after block the surgery started. In the case of unsuccessful block general anesthesia was induced. The aim of this study was to compare complication and success rates of caudal block and spinal anesthesia in awake preterm infants undergoing inguinal hernia repair