Objective: After the American Pain Society recognized pain as a fifth vital sign, many countries adopted similar pain screening approaches. The routine evaluation of pain has recently come to the agenda in Turkey, along with the important role played by nurses in pain evaluation, and hence, this study focuses on the opinions of nurses on the evaluation of pain as a fifth vital sign, their pain beliefs, and how their pain beliefs influence their opinions. Methods: This descriptive study was conducted in a City Hospital with the involvement of 223 nurses. A questionnaire and a Pain Beliefs Questionnaire were used for the collection of data, and the data were analyzed using descriptive statistics, and Mann-Whitney U-test, analysis of variance, and Kruskal-Wallis tests. Results: Of the respondent nurses, 31.8% of the nurses were working in medical inpatient clinics, and 56.5% stated that pain should not be evaluated as a fifth vital sign, giving the following reasons: if patients are in pain, they already report it (40.5%), and overwork and the lack of sufficient nurses (34.9%). There was no difference in the pain beliefs scores of the nurses who stated that pain should not be evaluated as a fifth vital sign (56.5%) and the scores of those who stated the opposite (43.5%) (P > 0.05). Conclusions: Most of the nurses do not think that pain should be evaluated as a fifth vital sign. Furthermore, the pain beliefs of nurses do not influence their opinions regarding the assessment of pain as a fifth vital sign.