Background: Unipolar mania is a putative subtype of bipolar disorder (BD) in which individuals experience recurrent manic but not major depressive episodes. Few studies of unipolar mania have been conducted in developed countries and none in the UK. This study aimed to identify and characterise people with unipolar mania in the UK and France. Methods: People with unipolar mania were ascertained using a South London UK electronic case register and a French BD case series. Each unipolar mania group was compared to a matched group of people with BD who have experienced depressive episodes. Results: 17 people with unipolar mania were identified in South London and 13 in France. The frequency of unipolar mania as a percentage of the BD clinical population was 1.2% for the South London cohort and 3.3% for the French cohort. In both cohorts, people with unipolar mania experienced more manic episodes than people with BD, and in the French cohort were more likely to experience a psychotic illness onset and more psychiatric admissions. Treatment and self-harm characteristics of people with unipolar mania were similar to people with BD. Limitations: The relatively small number of people with unipolar mania identified by this study limits its power to detect differences in clinical variables. Conclusions: People with unipolar mania can be identified in France and the UK, and they may experience a higher frequency of manic episodes but have similar treatment and self-harm characteristics as people with BD.