Dimensions of hearing aid outcome are explored in this paper. First, a variety of hearing aid outcome measures is defined including objective and subjective performance, objective and subjective benefit, satisfaction, and use. Following the definition of these terms, factor analysis is described as a statistical tool that can be of assistance in establishing the number and nature of the relevant dimensions of hearing aid outcome. Next, the results from three recent studies that included a variety of measures of hearing aid outcome are examined and factor analysis is applied to the data from each study. This examination leads to the conclusion that hearing aid outcome is a multidimensional construct, rather than unidimensional. The most complete description of hearing aid outcome will be obtained when including at least one measure of aided speech recognition performance, one or more measures of objective benefit in speech recognition, one or two subjective measures of sound quality or listening effort, and one measure of either subjective benefit, satisfaction, or use.