A multifrequency vibro-acoustography method is proposed that uses a multifrequency radiation stress produced by an array transducer driven with N ultrasound frequencies. The N ultrasound beams interfere at the system focus producing up to N(N-1)/2 unique difference frequencies in the radiation stress. The objective of this paper is to present the image formation theory in multifrequency vibro-acoustography systems with experimental validation. The radiation stress generated by sector array and annular array transducer systems is analyzed theoretically. We also used a computer phantom with small spheres to demonstrate the usefulness of multifrequency vibro-acoustography for microcalcification detection in breast imaging. The proposed method holds the potential for a large gain of information with no increase in scanning time when applied to conventional vibro-acoustography systems.