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The use of shallow pier foundations for rigid frame structures requires that the designer of the structure be able to predict any lateral spreading of the foundation so that the frame may be designed to accommodate any moment changes due to the spreading. Available procedures have not adequately defined the principal variables and no standard procedure has been developed for evaluating the horizontal coefficient of subgrade reaction. A mathematical relationship, based on the theory of beams on elastic foundations, is formulated for predicting the deflection of shallow piers subjected to horizontal forces near the ground line. The coefficient of horizontal subgrade reaction for use in the relationship was determined by in situ tests and related to pier size by theory of elasticity. Results of deflection tests on full scale piers are presented and compared to predicted deflections. The comparison indicates close agreement between actual and predicted deflections.