There has only been limited research into the predictors of readmission in bipolar disorder. We carried out a 1-year follow-up of patients discharged from a single mental health unit following admission for treatment of an acute bipolar episode. Of 519 patients followed up for 1 year, 167 (32.2%) were readmitted. There was no association between readmission and any drug regimen. Prescription of antidepressants at discharge was not associated with increased risk of readmission [odds ratio (OR): 0.99, 95% confidence interval (CI): 0.98-1.01]. Among demographic factors, only smoking (OR: 1.75, 95% CI: 1.14-2.75) and age range of 42-53 years (OR: 1.99, 95% CI: 1.15-3.43) conferred an increased risk of readmission. Individually optimized drug treatment regimens are equally effective in practice. It is not clear why smoking is associated with readmission.