Perfectionism is one of several personality traits associated with insomnia. Whilst research has examined the relationships between perfectionism and insomnia, the mediating role of dysfunctional sleep-related cognition (i.e. sleep-related worry and dysfunctional beliefs about the biological attribution of and consequences of poor sleep) has yet to be examined. This study aimed to determine whether aspects of multidimensional perfectionism were related to increased reporting of insomnia symptoms. In addition, the potential mediating role of dysfunctional sleep-related cognition and anxiety symptoms was examined. Members of the general population (N = 624) completed the Dysfunctional Beliefs and Attitudes About Sleep Scale, the Insomnia Severity Index, the Hospital Anxiety and Depression Scale, and the Multidimensional Perfectionism Scale. The results showed that perfectionism dimensions, anxiety symptoms, and dysfunctional sleep-related cognition were significantly associated with insomnia symptoms. Regression-based mediation analyses further showed that both dysfunctional sleep-related cognition and anxiety significantly mediated the associations between insomnia symptoms and three perfectionism dimensions (i.e. doubts about action, parental expectations, and parental criticism). The experience of perfectionistic tendencies, anxiety, and dysfunctional sleep-related cognition may initiate behavioural strategies (e.g. daytime napping) when faced with an acute sleep problem. However, these strategies may serve to transition insomnia from an acute to a chronic condition.