Bipolar disorder (BD) is associated with brain structural and cognitive abnormalities. There is a paucity of evidence regarding the evolution of these deficits over time. This study examined the relationship between age and brain morphology and cognition in patients with BD type I. Brain structural magnetic resonance imaging data were acquired using a 1.5T scanner from 71 BD patients and 82 age- and gender-matched controls and analysed using Statistical Parametric Mapping. In addition, participants were evaluated using the Wechsler Adult Intelligence Scale, Revised; the Wechsler Memory Scale, third edition; the Hayling Sentence Completion Task, a measure of response inhibition; and the Wisconsin Card Sorting Test, which reflects rule discovery and perseveration. We found a significant effect of age but not of diagnosis and no age-by-diagnosis interaction in global gray and white matter and cerebrospinal fluid volumes. There was no differential effect of age on the two diagnostic groups with respect to cognitive task performance. Our findings do not support differential age-related changes in brain structure and cognition in patients with bipolar disorder compared to healthy individuals. Cross-sectional studies are, however, limited and longitudinal data will be required to further explore this issue.