AIMS AND OBJECTIVES: To measure the diagnostic value of the Numeric Rating Scale by comparing it to a Verbal Rating Scale in older patients. BACKGROUND: Pain management in older patients is an important challenge because of their greater susceptibility to adverse effects of analgesics. Nurses play an important role in applying guidelines for postoperative pain treatment. However, effective pain management is dependent upon valid and reliable pain assessment. DESIGN: Cross-sectional study. METHODS: In total, 2674 older patients scored their postoperative pain on an 11-point numeric rating scale (NRS) and an adjective scale (VRS) including no pain, little pain, painful but bearable, considerable pain and terrible pain. The diagnostic value of different NRS cut-off values for administering analgesics is determined by an ROC curve. RESULTS: Sensitivity of NRS > 3 for 'unbearable' pain in older patients was 72% with a specificity of 97·2%. With a cut-off point NRS > 4, sensitivity increased to 83%, while specificity was 96·7%. With a cut-off point NRS > 5, sensitivity was 94%, while specificity was 85%. A high proportion (75%) of older old patients (≥ 75 years) with 'painful but bearable' considers NRS 4, 5 and 6 to this VRS category. CONCLUSION: Using an NRS cut-off point > 3 or > 4, a large group of older patients with 'bearable' pain would incorrectly classified as 'unbearable'. When we make the assumption that bearable pain means no wish for additional analgesics, this misclassification might result in overtreatment with analgesics, while 3% would be undertreated. With NRS cut-off point > 5, 6% have a risk of overtreatment and 15% of undertreatment. RELEVANCE TO CLINICAL PRACTICE: Nurses should not rely solely on the NRS score in determining pain treatment; they need to communicate with older patients about their pain, the need for analgesics and eventual misconceptions about analgesics.