The ability of Additive Manufacturing (AM) processes to fabricate complex geometries is somewhat hindered by an inability to effectively validate the quality of printed complex parts. Furthermore, there are classes of part defects that are unique to AM that cannot be efficiently measured with standard Quality Control (QC) techniques (e.g., internal porosity). Current QC methods for AM are limited to either destructive evaluation of printed test coupons, or expensive radiation-based scanners of printed parts for non-destructive evaluation. In this paper, the authors describe their use of impedance-based structural monitoring to indirectly measure printed part abnormalities. By bonding a piezoceramic (PZT) sensor to a printed part, the measured electrical impedance of the PZT can be directly linked to the mechanical impedance of the part. By observing deviations in the mechanical impedance of the part, as determined by this quick, non-intrusive electrical measurement, one is able to detect the existence of part defects. In this paper, the authors explore the effectiveness and sensitivity of the technique as a means for detecting of a variety of defect types and magnitudes.