Objectives: Adequate pain management of emergency department (ED) patients is an important clinical goal. Pain perception in ED patients with headache has been reported to differ from that of other patients with pain. If this were true in our setting, we might interpret pain scores and response to analgesics differently. We compared pain perception in ED patients without pain, patients with headache, and patients with non-headache pain who had blood pressure (BP) measurement and intravenous (IV) cannulation for any reason. Methods: The study design was approved by our hospital's Ethics Committee. The patients were asked to describe their pain while undergoing BP measurement and IV cannulation with a 0 through 10 (11-point) numerical rating scale. Pain scores were analysed according to the patient's group: no pain, headache pain, or non-headache pain. Results: For the 278 participating patients (95 patients without pain, 77 patients with headache, and 106 patients with non-headache pain), the pain scores as reported during BP measurement and IV cannulation was not significantly different between the patient groups. On sub-group analysis, females reported higher pain scores during IV cannulation than males (2.8 +/- 2.6 vs. 2.3 +/- 1.9, p=0.06). In addition, married patients had higher pain scores than unmarried patients during both BP measurement (1.31 vs. 1.03, p=0.004) and cannulation (2.73 vs. 2.16, p=0.089). Conclusion: The differences in pain experienced in patients with or without headache or other causes of pain during IV cannulation and BP measurement were minor. Based on our findings, gender and marital status should be recorded during studies recording pain levels in ED patients. (Hong Kong j.emerg.med. 2011;18:131-135)