OBJECTIVES: This study assesses the long-term treatment outcomes of 204 ambulatory patients diagnosed with bipolar disorder who are taking daily dose of lithium carbonate with or without mood stabilizers for a span of at least 2 years.  METHODS:   Semi-structured questionnaires were used by psychiatrists and primary care physicians to monitor treatment outcomes parameters of bipolar disorder as prescribed by the British Association for Psychopharmacology.  RESULTS: Female patients aged 25 years and above were found to be at great risks for poor treatment outcomes. Supplementing lithium carbonate with quetiapine, lamotrigine or valproic acid significantly reduced the frequency of hospitalization, manic episodes and affective behaviors in more than 50% of the population but did not significantly reduced the risks for suicidal tendencies. No significant improvement was observed in patients supplemented with carbamazepine. Adverse drug reactions, age and economic class, with preference for female patients, appear to positively influence adherence to medications and mood stabilization.  After 2 years of treatment, lithium monotherapy, based on GAS rating, gave a good outcome in only 31% of the population while treatment with lithium supplemented with valproic acid or quetiapine gave a good outcome in 72% of the cases. Smoking and alcohol abuse were found to be associated with poor outcomes.  CONCLUSIONS: The findings show that supplementation of lithium carbonate with quetiapine, valproic acid and lamotrigine improved treatment outcomes in majority of the patients. The large variance in the treatment outcomes between monotherapy and combination treatments suggests underlying differences in the pathophysiology of bipolar disorder.