Medication nonadherence is a key clinical concern in bipolar disorder (BD) across the life span. Cognitive deficits in older adults with BD may hinder medication management ability, which, in turn, may lead to nonadherence. Using an innovative performance-based measure of medication management ability, the Medication Management Ability Assessment (MMAA), we compared performance of 29 middle-aged older community-dwelling outpatients with BD who were clinically stable (mean age, 61 years; SD, 11 years; range, 45-86 years) with those of 59 normal control subjects (NCs) and 219 outpatients with schizophrenia. The MMAA is a role-play task that simulates a medication regimen likely to be encountered by older adults. Within the BD group, we examined the relationships of MMAA scores to demographic, psychiatric symptoms severity, and the Mattis Dementia Rating Scale (DRS) scores. The BD group made 2.8 times the errors on the MMAA than NCs (BD group, 6.2; SD, 5.5 vs NCs, 2.2; SD, 2.5) and did not significantly differ from the Schizophrenia group in errors on the MMAA. Errors in the BD group were more likely to be taking in too few medications as taking in too many. Within the BD group, a significant correlation was seen between MMAA scores and the DRS Total score, but not with age, education, Brief Psychiatric Rating Scale, Hamilton Depression Rating Scale, number of psychiatric medications, or medical conditions. Among DRS subscales, the Memory Subscale correlated most strongly with MMAA errors. This small cross-sectional study suggests that deficits in medication management ability may be present in later-life BD. Neurocognitive deficits may be important in understanding problems with unintentional nonadherence.