In this paper we paper evaluate the effectiveness of eight sessions of cognitive analytic therapy (CAT) for treating obsessive morbid jealousy (OMJ), using a mixed-methods A/B with followup single-case design. Ideographic jealousy measures were collected throughout baseline (2 sessions), treatment (6 sessions) and follow-up phases (one session), creating a 160-day time series. Nomothetic measures were completed at assessment, end of treatment and at followup. A structured qualitative interview was completed. Significant reductions to idiographic jealousy measures occurred during the treatment phase, with these gains maintained over followup. The intensity of the jealousy shifted from moderate to mild and this change was attributed to CAT. Methodological issues and future directions for the treatment of OMJ are discussed.