Background: Patients postoperative pain is often underestimated. Untreated or undertreated pain decreases the chance of optimal recovery after surgery. Pain assessment is an important factor of efficient pain relief. Aim: The aim of the literature study was to describe factors of importance for nurses´ assessment of postoperative pain in patients. Method: A literature study was done where qualitative and one quantitative article was reviewed. Eleven articles were analyzed. Results: The analysis resulted in four categories; nurses´ ability to assess patients´ postoperative pain through verbal communication, nurses´ ability to assess patients’ postoperative pain through non-verbal communication, nurses knowledge and experience and nurses attitudes. Discussion: Nurses ability to receive patients´ pain signals varies. Assessment of patients´ postoperative pain is seldom planned, but rather randomly made. Nurses seldom use tools for pain assessment; instead they rely on what the patients tell them and assess the pain from that information. Nurses with a specific pain education have a more positive attitude towards tools for pain assessment. Conclusion: Nurses attitudes affect the ability to communicate both verbal and non-verbally. Nurses´ attitudes are of importance for assessment of postoperative pain in patients. Education has shown itself to have a positive effect on nurses´ attitudes towards pain assessment and tools for assessing the pain.