Background The use of nurses for telephone-based triage in out-of-hours services is increasing in several countries. No investigations have been carried out in Norway into the quality of decisions made by nurses regarding our priority degree system. There are three levels: acute, urgent and non-urgent.

Methods Nurses working in seven casualty clinics in out-of-hours districts in Norway (The Watchtowers) were all invited to participate in a study to assess priority grade on 20 written medical scenarios validated by an expert group. 83 nurses (response rate 76%) participated in the study. A one-out-of-five sample of the nurses assessed the same written cases after 3 months (n=18, response rate 90%) as a test–retest assessment.

Results Among the acute, urgent and non-urgent scenarios, 82%, 74% and 81% were correctly classified according to national guidelines. There were significant differences in the proportion of correct classifications among the casualty clinics, but neither employment percentage nor profession or work experience affected the triage decision. The mean intraobserver variability measured by the Cohen kappa was 0.61 (CI 0.52 to 0.70), and there were significant differences in kappa with employment percentage. Casualty clinics and work experience did not affect intrarater agreement.

Conclusion Correct classification of acute and non-urgent cases among nurses was quite high. Work experience and employment percentage did not affect triage decision. The intrarater agreement was good and about the same as in previous studies performed in other countries. Kappa increased significantly with increasing employment percentage.