A textile yarn processing machine, such as a two-for-one twister or the like, having respective yarn processing stations is provided with an improved yarn monitoring system for stopping the operation of the yarn processing station in response to the absence of a yarn running therethrough, as for example, upon the occurrence of a yarn breakage. The improved yarn monitoring system of the present invention is constructed generally as follows: A yarn sensor is constructed and mounted so as to be held in an operative setting by yarn tension when the yarn is running in normal operating condition and to be released in the event of the release of such tension, as upon a yarn breakage. A switching mechanism is provided for stopping the operation of the yarn processing station, and means is provided for operably connecting the yarn sensor to the switching mechanism for actuating the switching mechanism upon the release of the yarn sensor from its operative setting. These devices cooperate with a time delay means which is actuable upon restarting the yarn processing station for permitting a further actuation of the switching mechanism only after a predetermined period of time has elapsed to thus allow the yarn processing station to resume a normal, stabilized operating condition and to thereby avoid inadvertent and undesirable actuation of the switching mechanism prior to the yarn processing station reaching such a stabilized operating condition.