Objective: The aim of this study was to evaluate health-related quality of life (HRQoL) in adults with hearing impairment in Finland before and after hearing rehabilitation. Design: The study was prospective with hearing-aid rehabilitation as the intervention. The data was collected, using the 15D instrument, before and six months after hearing-aid rehabilitation. The data was analysed using t-tests and multiple linear regression methods. Study sample: The study sample included 949 adults with hearing impairment, and the control group included a sample of age- and gender-standardized general population. Results: The study population had significantly poorer HRQoL on most dimensions of the 15D when compared to the control group both before and after hearing-aid rehabilitation. Hearing-aid rehabilitation resulted in improved mean scores on the dimensions of hearing and in the overall 15D score that were statistically significant, although the mean improvement in the overall score was marginal. Self-reported hearing ability can better predict the change in HRQoL, as a result of a hearing aid, when compared with measured hearing sensitivity. Conclusions: The study supports the hypothesis that on average, use of a unilateral hearing aid results in improved subjective hearing and marginal improvement in HRQoL in adults with hearing impairment.