Jealousy is a common emotion which can be considered pathological in some circumstances. The term ‘morbid jealousy’ has been used to signify this abnormal or extreme condition. However, the literature on morbid jealousy is sparse and the empirical data fragmentary. The aims of this paper are to briefly review the concept, to define the dimensions of the disorder and to apply a cognitive-behavioural framework to it. Such a summary paper is timely, to draw together the different aspects of the problem and to provide a theoretical base from which to generate further research.