Purpose: The goal of this study was to find factors for refining candidacy criteria for bilateral hearing aid fittings. Clinical files of 1,000 consecutive hearing aid fittings were analyzed. Method: Case history, audiometric, and rehabilitation data were collected from clinical files, and an extensive questionnaire on long-term outcome measures was conducted. After at least 2 years of hearing aid use, 505 questionnaires were returned. In order to compare differences in benefits between unilateral and bilateral fittings, two subgroups were composed in which most relevant variables (age, degree of hearing loss, and audiometric asymmetry) were matched for unilateral fittings (n = 212) and bilateral fittings (n = 477). Results: The bilateral group had significantly higher benefit scores than the unilateral group for detection, speech intelligibility in reverberation, and localization, but poorer scores for comfort of loud sounds. The benefit of bilateral hearing aids was not significantly related to the level of technology of the hearing aids. Conclusion: The analysis of the relation between objective parameters and the subjective outcome measures showed that candidacy for a successful bilateral fitting could not be predicted from age, maximum speech intelligibility, employment, exposure to background noise, or social activities.