Prior studies demonstrate structural abnormalities of cerebellar vermis in adult bipolar patients. Cerebella of 16 young bipolar patients (mean age ± S.D. = 15.5 ± 3.4) and 21 healthy controls (mean age ± S.D. = 16.9 ± 3.8) were examined using magnetic resonance imaging. The volumes of right, left and total cerebellum, vermis, and areas of vermal regions V1 (lobules I-V), V2 (lobules VI-VII), and V3 (lobules VIII-X) were measured. Analysis of covariance, with age, gender, and intra-cranial brain volume as covariates, revealed no significant differences in cerebellum or vermis measures between patients and controls; however, there was a trend to smaller vermis V2 areas in patients (p=0.06). The number of previous affective episodes and vermis area V2 were inversely correlated (partial correlation coefficient = −0.97, P = 0.001) in the male bipolar patient group. Our results are preliminary, but consistent with the findings from studies in adult bipolar patients suggesting the involvement of structural changes in cerebellar vermis in the pathophysiology of bipolar disorder.