The purpose of this study was to investigate normal body temperature in adult men and women. A systematic review of data was performed. Searches were carried out in MEDLINE, CINAHL, and manually from identified articles reference lists. Studies from 1935 to 1999 were included. Articles were classified as (1) strong, (2) fairly strong and (3) weak evidence. When summarizing studies with strong or fairly strong evidence the range for oral temperature was 33.2-38.2 degreesC, rectal: 34.4-37.8 degreesC, tympanic: 35.4-37.8 degreesC and axillary: 35.5-37.0 degreesC. The range in oral temperature for men and women, respectively, was 35.7-37.7 and 33.2-38.1 degreesC, in rectal 36.7-37.5 and 36.8-37.1 degreesC, and in tympanic 35.5-37.5 and 35.7-37.5 degreesC. The ranges of normal body temperature need to be adjusted, especially for the lower values. When assessing body temperature it is important to take place of measurement and gender into consideration. Studies with random samples are needed to confirm the range of normal body temperature with respect to gender and age.