Objective: To analyze the frequency of unintended hypothermia in patients undergoing elective surgery in the perioperative period, scoring its relationship with the type of anesthesia. Method: Cross-sectional, descriptive, and quantitative approach study with a sample of 53 patients aged between 18 and 90 years, developed in a surgical center of a private hospital in the Midwest region of the Sao Paulo State. Results: The female gender appeared as a major variable (79.3%), and 96.3% of the assessed patients presented hypothermia, ranging from mild to moderate. The number of hypothermic patients undergoing spinal anesthesia was higher when compared to those undergoing general anesthesia, both in the operation room (93.5%) and in the postanesthetic room (96.8%). Conclusion: Hypothermia is a common event that affects a large portion of patients undergoing surgical procedures, so it is essential that nurses early identify the occurrence of this phenomenon to provide a qualified and safe care to these patients.