A theoretical analysis is conducted on the kinetics of diffusional release of an ellipsoidal drug delivery device. By choosing appropriate coordinates, the present analysis is applicable to devices of various shapes such as prolates, oblates, disks, and rod-like shapes. We show that, regardless of the shape of a device, the cumulative fraction of drug release can be expressed in a concise, yet general form. The performance of a widely adopted empirical relation in the literature for the description of the temporal variation in the amount of drug released is compared with that of the present study. The result of numerical simulation reveals that, although the former is satisfactory for the case when the cumulative fractional drug release is below 60%, it may lead to inappropriate description for the release kinetics considered in this study. (c) 2005 Elsevier Ltd. All rights reserved.