Background Recognising early warning signs (EWS) of mood changes is a key part of many effective interventions for people with Bipolar Disorder (BD). This study describes the development of valid and reliable checklists required to assess these signs of depression and mania.MethodsChecklists of EWS based on previous research and participant feedback were designed for depression and mania and compared with spontaneous reporting of EWS. Psychometric properties and utility were examined in 96 participants with BD.ResultsThe majority of participants did not spontaneously monitor EWS regularly prior to use of the checklists. The checklists identified most spontaneously generated EWS and led to a ten fold increase in the identification of EWS for depression and an eight fold increase for mania. The scales were generally reliable over time and responses were not associated with current mood. Frequency of monitoring for EWS correlated positively with social and occupational functioning for depression (beta = 3.80, p = 0.015) and mania (beta = 3.92, p = 0.008).LimitationsThe study is limited by a small sample size and the fact that raters were not blind to measures of mood and function.ConclusionsEWS checklists are useful and reliable clinical and research tools helping to generate enough EWS for an effective EWS intervention.