The International Outcome Inventory for Hearing Aids (IOI-HA) is a seven-item questionnaire designed to be generally applicable in evaluating the effectiveness of hearing aid treatments. The inventory was developed to facilitate cooperation among researchers and program evaluators in diverse settings. It is brief and general enough to be appended to other outcome measures that might be planned in a particular application, and will provide directly comparable data across otherwise incompatible projects. For this plan to be successful, it is essential to generate psychometrically equivalent translations in the languages in which hearing aid research and treatment assessments are performed. This article reports the psychometric properties of the inventory for the original English version. The items are reasonably internally consistent, providing adequate statistical support for summing the scores to generate a total outcome score. However, for maximum internal consistency, it would be desirable to generate two scores for the inventory.