BACKGROUND: Postoperative pain remains a problem for many patients. One of the reasons could lie in the insufficient evaluation of pain and analgesia. This study was designed to obtain more insight in the performance of nurses and physicians in evaluating patients' postoperative pain and pain relief. METHODS: Forty patients hospitalised in one surgical unit and the 8 nurses and the 2 surgical residents in charge of this unit were investigated. Patients were asked to assess on a visual analogue scale the intensity of their pain and their pain relief at rest, on coughing and globally since the operation, on the first and second postoperative days and the day before hospital discharge. Separately, the nurses and the physicians were asked to evaluate the pain intensity and the pain relief for each patient involved. A MANOVA and a multiple comparisons test with Bonferroni adjustment were used. RESULTS: At rest, only nurses underestimated pain intensity on the day before hospital discharge. On coughing, physicians underestimated pain intensity in all 3 assessments, whereas nurses only in the 3rd assessment (on the day before hospital discharge). Globally, physicians underestimated pain intensity in all 3 assessments, nurses in the 2nd and the 3rd assessment. Only physicians overestimated pain relief on coughing on the day before hospital discharge and globally in all 3 assessments. Surprisingly, the pain scores rated by the patients before hospital discharge were high. CONCLUSION: The results of this survey suggest that assessment of pain and pain relief is inadequately done by both physicians and nurses. This emphasises the importance of a better training, and a systematic assessment of pain intensity and pain relief.