An insertion set is provided for transcutaneous placement of a sensor such as a glucose sensor at a selected site within the body of a patient. The insertion set comprises a slotted insertion needle extending through a mounting base adapted for mounting onto the patient's skin. A flexible thin film sensor includes a proximal segment carried by the mounting base and defining conductive contacts adapted for electrical connection to a suitable monitor, and a distal segment protruding from the mounting base with sensor electrodes for transcutaneous placement. The proximal and distal segments of the sensor are linearly offset or misaligned, with the distal segment fitted within the insertion needle for transcutaneous sensor placement with the needle as the mounting base is pressed onto the patient's skin. The insertion needle can then be withdrawn to leave the sensor distal segment at the selected insertion position with the sensor electrodes in contact with patient blood or other extracellular fluid.