An integro-modal approach is presented in this paper for computing the acoustic properties of irregular-shaped cavities. The method consists of discretizing the whole cavity into a series of subcavities, whose acoustic pressure is decomposed either over a modal basis of regular subcavities or over that of the bounding cavities in the case of irregular-shaped boundaries. An integral formulation is then established to ensure continuity of both pressure and velocity between adjacent subcavities using a membrane with zero mass and stiffness. To some extent, the method provides a combined approach retaining the advantages of both the acoustoelastic method (AEM) and the Green’s function method (GFM). Numerical and experimental results are presented demonstrating the efficiency and accuracy of the suggested technique. Comparisons with other existing methods are also made. It is shown that good accuracy on the computation of cavity modes can be obtained using a very limited number of subcavities.