In 47 patients admitted to the coronary care unit (CCU) at Sahlgren's Hospital in Göteborg, Sweden, due to acute myocardial infarction (MI) the intensity of pain independently assessed by the patient and by the nurse on duty was evaluated during the first 24 hours in CCU. Pain was assessed according to a modified numerical rating scale graded from 0-10, where 0 meant no pain and 10 meant the most severe pain. A positive correlation between the patients' and nurses' assessments was found (r = 0.76; P less than 0.001). However, the nurses under-estimated the patients' pain in 23% of the situations and over-estimated it in 20%. Over-estimation was particularly found when heart rate and blood pressure increased. Many patients scoring their pain to fairly high degrees were not given pain-relieving treatment. Treatment with morphine did not cause substantial pain relief in a substantial number of patients. A significantly positive correlation was found between the patients' and nurses' assessments of pain, although under-estimation as well as over-estimation occurred. A few patients with severe pain were not treated and when treatment was given it was often ineffective.