Abstract: A rectal thermometer for measuring the temperature of a patient including a disk or oval-shaped member having a circumferential edge and first and second sides. Along the edge is a temperature display that is viewable during the temperature taking process without having to first remove the thermometer from the anal canal. The first and second sides form a concave shape and include an actuation switch and battery compartment. Connected to the main housing via a probe guard portion is a controlled-depth temperature sensing probe which can be fully inserted into the anal canal without concern for over-insertion. The probe guard portion, which may be formed of flexible material, is adapted such that its thickness gradually increases proximate the main housing and serves to slow down the entry of the probe within the anal canal. Finally, the rectal thermometer includes a holder having a proximal end for covering the housing and a distal end for covering the probe.