Hearing loss has been associated with poor vitamin B12 status in some, but not all studies. This study examined a possible relationship between age-related hearing loss and poor B12 status in 93 older adults using different indices of B12 status. Hearing loss was defined as pure-tone average threshold > 25 decibel hearing level. Participants with methylmalonic acid (MMA) > 271 nmol/L at baseline received 1,000 g/d, and those with MMA < or = 271 nmol/L were randomly assigned to receive 0, 25, or 100 microg/d of B12. In a series of logistic regression analyses, compared with participants with normal hearing, those with impaired hearing had a significantly higher serum mean MMA concentrations in the best and the worst ears and a higher prevalence of elevated MMA (> 271 nmol/L) in the worst ear only. Thus, elevated MMA concentration may be associated with hearing loss in older adults. However, short-term B12 supplementation was unrelated to improvements in hearing status in B12-deficient individuals.