BACKGROUND: Despite readily available evidence to guide practice, children continue to experience moderate to severe pain in hospital postoperatively. Reasons for this may include attitudes of nurses toward pain management and their lack of knowledge in key areas. AIMS: To identify nurses' knowledge and clinical practice of pediatric postoperative pain management and whether there is a link between knowledge and practice. DESIGN AND SETTING: A descriptive cross-sectional study including a questionnaire and observations was conducted in postanesthesia care (recovery) units in six university hospitals in Norway. METHODS: Nurses completed the Pediatric Nurses' Knowledge and Attitudes Survey Regarding Pain Questionnaire-Norwegian Version (PNKAS-N). We observed their clinical practices using a structured observational tool and field notes. RESULTS: Nurses completed the PNKAS-N (n = 193) and were observed (n = 138) giving postoperative care to 266 children (70 hours per unit, 416 hours in total). The mean PNKAS-N score was 29 (standard deviation 4.2) of 40. We identified knowledge deficits, mainly in pharmacologic management, such as in risk of addiction and respiratory depression. We found that, overall, pain was assessed using validated tools in 19% of the children; this fell to 9% in children aged <5 years. More than 66% of children received an inadequate dose of morphine postoperatively. CONCLUSION: Nurses have knowledge deficits about pediatric pain management and do not always use their knowledge in practice, particularly in relation to pain assessment. There is a need to improve nurses' knowledge of pediatric pain management and to test interventions that support the use of that knowledge in practice.