We aimed to compare the accuracy of digital axillary thermometer (DAT), rectal glass mercury thermometer (RGMT), infrared tympanic thermometer (ITT) and infrared forehead skin thermometer (IFST) measurements with traditional axillary glass mercury thermometer (AGMT) for intermittent temperature measurement in sick newborns. A prospective, descriptive and comparative study in which five different types of thermometer readings were performed sequentially for 3 days. A total of 1989 measurements were collected from 663 newborns. DAT and ITT measurements correlated most closely to AGMT (r = 0.94). The correlation coefficent for IFST and RGMT were 0.74 and 0.87, respectively. The mean differences for DAT, ITT, RGMT and IFST were +0.02°C, +0.03°C, +0.25°C and +0.55°C, respectively. There were not any clinical differences (defined as a mean difference of 0.2°C) between both mean AGMT&DAT and AGMT&ITT measurements. Our study suggests that tympanic thermometer measurement could be used as an acceptable and practical method for sick newborn in neonatal units.