Circumferential frictional sliding between the matrix and fibers in a titanium aluminide matrix composite has been measured during transverse loading using a displacement mapping method based on differential image analysis. Sliding was detected over all of the interface before initiation of the cracks that eventually caused failure. The results are compared with recent analytical solutions for the interfacial stresses that account for near-neighbor fiber interactions. The location at which sliding initiated coincided with the predicted position of maximum shear stress, while the calculated magnitude of the shear stress when sliding began was equal to the previously measured resistance to frictional sliding in the longitudinal direction. The results indicate that circumferential sliding has a strong influence on the local stress concentrations that lead to failure.