The field of dissociation is receiving increasing attention, despite a lack of coherent conceptualisation of the construct. Advances in the field would be aided by a measure that reflects service user experiences of dissociative experiences and can be easily scored. The current study describes the development of a new measure of dissociation (Dissociative Experiences Measure, Oxford; DEMO) that aims to fulfil these criteria. The study follows an exploratory, data-driven, measure development design. Resource searching and feedback from clinicians (n = 3) and service users (n = 6) were used to develop an extensive item pool. An online sample (n = 691) provided data for a factor analysis of the item pool. Factor analysis produced a measure with five subscales: ‘unreality’, ‘numb and disconnected’, ‘memory blanks’, ‘zoned out’, and ‘vivid internal world’. Further analysis indicated that the new measure has high internal consistency, and high convergent, divergent, and discriminant validity. The DEMO shows promise as an up-to-date clinical and research tool for the assessment of dissociative experiences. These results are preliminary, and further validation of the measure with a clinical sample is required.