Patients will be admitted to the NIH Clinical Center for initiation and titration of Lithium until high therapeutic levels currently accepted for the treatment of Bipolar affective disorder are achieved (1.0-1.2 mmol/L) or a maximum tolerated dose. During their admissions, they will have neurological evaluations, ataxia and tremor evaluations, timed-up-and-go testing, quality of life assessment, questionnaires evaluating sleep, balance confidence and depression, memory testing, alertness assessment and quantitative balance/sway evaluations. Parameters and side effect profiles will be assessed at baseline, 1 month (plus or minus 5 days) and 3 months (plus or minus 5 days) after achievement of therapeutic levels. They will also have an exit evaluation one month (plus or minus 5 days) after discontinuation of Lithium also at the NIH. For their baseline evaluation and titration, patients will be admitted to the NIH for 4 weeks plus or minus 2 weeks. Evaluation at 1 month (plus or minus 5 days) and 3 months (plus or minus 5 days)