Purpose: This article aimed to document longitudinal changes in auditory function, including measures of temporal processing, and to examine the associations between observed changes in auditory and cognitive function in middle-aged and older adults. Method: This was a prospective longitudinal study of 98 adults (66 women) with baseline ages ranging from 40 to 85 years. The mean interval between T1 baseline and T2 follow-up measurements was 8.8 years with a range of 7-11 years. Measures of hearing threshold, gap detection, and auditory temporal-order identification were completed at T1 and T2. Cognitive measures completed at T1 and T2 were the 13 scales of the Wechsler Adult Intelligence Scale--Third Edition. Three approaches were taken to analyze these data: (a) examination of changes over time in group performance, (b) correlations and slopes between auditory and cognitive measures to examine concomitant rates of decline over the 9-year T1-to-T2 period, and (c) regression analyses examining associations between auditory performance at T1 and cognitive performance 9 years later at T2. Results: For the group data, there were significant declines in hearing loss, gap-detection thresholds at one frequency, and process-type measures of cognitive function from T1 to T2 matching the trends in the baseline cross-sectional data. Regression analyses of the longitudinal data revealed the strongest connection between auditory temporal-order processing and cognitive processing typically explaining 10%-15% of the variance. Conclusions: A significant amount of variance in rates of cognitive decline, T1 to T2, and subsequent cognitive performance (T2) was explained by measures of auditory function. Although hearing loss occasionally emerged as a significant factor, auditory temporal-order identification emerged much more frequently as the auditory measure most strongly associated with cognitive function.