A multi-configuration electronic thermometer operates in any of a plurality of modes, including a rectal mode, an underarm mode and an oral mode. A probe arm swings about an axis that is located closer to one end of an elongate thermometer body than it is to the other end. In a first, rectal configuration, only a limited length of the probe arm extends beyond a front end of the thermometer body. In a second configuration, the probe arm is swung to a position such that its free end is farther from a second end of the body than it was from the first end while in the first configuration. The probe arm is spring-loaded to lock to a user-selected one of the configurations and is torsionally biased to the more compact, first configuration. Different sensing algorithms are used depending on the mode selected.