This randomised controlled study tested whether adding imagined to live exposure plus ritual prevention would enhance gains in obsessive-compulsive disorder (OCD).

Out-patients with OCD were randomly allocated to either have nine sessions of daily live self-exposure and ritual prevention to external cues alone (Ex) (n = 23) or to have, in addition to Ex, daily self-exposure to the imagined internal cues of the consequences of not ritualising (group Exi) (n = 23). All patients had the same sessional exposure time of 1 h 30 min (Exi 1 h live, 30 min imagined; Ex 1 h 30 min live), and had to practise either Exi or Ex daily for the same duration and to keep diaries of that self-exposure homework throughout treatment. Patients were followed up to week 32. Outcome measures were YBOCS for rituals and obsessions, compulsion checklist, target rituals and obsession, general anxiety, depression (Beck, Hamilton), work and social disability, clinical global impression (CGI).

At weeks 4, 9, 20 and 32 the two groups improved similarly with no significant difference between them, neither for washers nor for checkers. Imagined exposure was more difficult to do than live exposure and there were more drop-outs.

Daily imagined exposure to internal cues did not enhance exposure to external cues. Perhaps longer imagined exposure would have been more enhancing.