Lamb waves have been used with considerable success to detect and quantify damage in aerospace, mechanical and civil structures. The mathematical representation of these particular waves is well known and understood, and we build upon these results in an attempt to detect and quantify scattering due to the presence of a spherical corrosion pit on the surface of a layer. By using the usual superposition argument, the total field consists of the incident and scattered fields, where the latter is generated by tractions on the surface of the cavity, which are obtained from the stress fields of the incident Lamb wave. In the approximation advanced in this paper these tractions are then represented by body forces in the interior of the intact layer. The acoustic radiation from the resultants of these body forces approximates the scattered field. The resultant forces are decomposed in symmetric and anti-symmetric systems, which generate symmetric and anti-symmetric radiating modes. The time-harmonic elastodynamic form of the reciprocity theorem is employed in an elegant way to obtain an analytical solution to the scattered field amplitudes. As our damage metric we obtain the ratio of scattered to incident Lamb mode amplitudes, which in a closed form include material properties, geometry of the pit and layer, and angular frequency of the incident wave. Results of this study yield graphical representations for the magnitude of the out of plane scattered displacements with respect to pit geometry, and has the potential to lead to a unique solution of the inverse problem.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.