Our knowledge about the content of the clinical knowledge used by nurses in a surgical recovery unit for assessment of postoperative pain is fairly limited. The aim of the present study was to analyse and describe the variations of nurses' conceptions of the impact of clinical experience on competence in post-operative pain assessment. The informants consist of critical care nurses. A phenomenographical approach has been applied to tape-recorded interview data. The results reveal that clinical competence in pain assessment was described in three categories: (a) to be able to see; (b) to be able to differentiate; (c) to be able to give. The observations articulate what nurses perceive that they have learnt from experience in performing many clinical pain assessments and point to some difficulties in using a single-data source for the development of valid and truthful professional knowledge. In the development of professional experience, it is of the utmost importance to be able to change perspective from what is most frequent and general to what is special and unique, to base one's standpoint on the individual patient's experience and integrate this with previous professional experience.