The Liverpool Infant Distress Scale (LIDS) was initially designed to assess behaviours reflecting pain in neonates following surgery. This paper reports a further development of the validity and reliability of LIDS and its use as a measure of neonatal behaviour. In the first stage of validity testing the LIDS scores of infants prior to administration of analgesia were compared to LIDS scores postanalgesia. Significantly lower scores were recorded following analgesia. The second stage of validity testing compared LIDS scores of a control group of neonates with those undergoing surgery, each over 43 hours. A significantly lower score on LIDS was found for the control group of infants compared to the surgical group, providing support for validity. Internal consistency was high, providing support for reliability. By providing detailed description of neonatal behaviours LIDS may assist nurses in the identification and objective quantification of neonatal behaviour, the context of which will govern intervention. The efficacy of such interventions may also be measured using LIDS.