This study compares spinal anaesthesia for inguinal herniotomy in preterm infants in the lateral or sitting position. Thirty patients were randomly divided into two equal groups. One hour before spinal anaesthesia, a eutetic mixture of local anaesthetic cream was applied to the lower lumbar spine. Sedation with nitrous oxide 50% in oxygen was given to all patients before and during induction of spinal anaesthesia, and throughout surgery. Lumbar punctures were performed at the L4-5 interspace using a 2.5 cm 22 G needle. Isobaric bupivacaine 0.5% with epinephrine 1 : 200 000 at a bupivacaine dose of 1 mg.kg-1 was injected in the lateral or sitting position. Measurements included heart rate, blood pressure, oxygen saturation, maximum sensory block height and duration of motor block and analgesia. There were no statistically significant differences between the groups in any measured parameters. Median [range] maximum block height was T5[T4-T7] in the lateral group and T5[T4-T5] in the sitting group. The median [range] duration of motor blockade was 67 [50-85] min in the lateral group and 63 [50-80] min in the sitting group. Our results indicate that in preterm infants sedated with nitrous oxide, spinal anaesthesia for inguinal herniotomy performed with isobaric bupivacaine 0.5% at a dose 1.0 mg.kg-1 in the lateral or sitting position is equally effective and is associated with minimal side effects.