Harvey (2002) developed a model of insomnia that has advanced the understanding of cognitive processes involved in the maintenance of this problem. Despite the high co-morbidity of insomnia with mental health problems, such as anxiety, the relevance of the cognitive processes specified in the model to people with insomnia as well as other mental health problems is yet to be established. This was the subject of investigation in the present study. A between-subjects design was used to compare people with insomnia and co-morbid anxiety (insomnia plus anxiety) with people with insomnia only (insomnia only), and with good sleepers on measures of mental arousal prior to sleep, thought control strategies employed, and unhelpful beliefs about sleep. Results showed that participants with insomnia plus anxiety were comparable to participants with insomnia only, and significantly different from good sleepers on all measures. The research suggests that the cognitive processes thought to maintain insomnia in people without other co-morbid mental health problems may also maintain insomnia in people with co-morbid anxiety disorders.