An apparatus and a method for checking the position and/or dimensions of a workpiece, more specifically dimensions of teeth (T) of gears, make use of a touch trigger probe (1) having a determined pre-stroke (Rp) and driving and detecting devices (11) to check a position of the probe in a reference system (9). A feeler (7) of the probe approaches and contacts a surface (S) of the tooth to be checked along a checking direction (Dc) that is inclined with respect to a direction (Do) perpendicular to the same surface. The position of a point (P) on the surface of the tooth is detected on the basis of the position (XC) of the center (C) of the feeler when the contact takes place that, in its turn, is based on the indication provided by the driving and detecting devices and a processing that takes into account the pre-stroke and the angular arrangement (P) of the checking direction. Specific methods for checking the tooth thickness or other dimensions of the gear include additional steps.