Associations between delusions and abnormal behaviour were retrospectively assessed in a sample of 83 consecutively admitted deluded subjects. All were interviewed about events in the previous month using a new measure of delusional phenomenology and action. For 59 subjects this information was supplemented by informant interviews. Clinical consensus was reached concerning the probability that actions reported by informants were linked to delusions. Half of the sample reported that they had acted at least once in accordance with their delusions. Violent behaviour in response to delusions was uncommon. Information provided by informants suggested that some aspect of the actions of half of the sample was either probably or definitely congruent with the content of their delusions. However, there was no link between self-reports and informants' reports of such action. A latent class analysis of self-reported delusional action suggested three classes of action, namely aggressive to self or other, defensive action, and either none or single action. Self-reported action was associated with delusions of catastrophe. Informant data suggested that persecutory delusions were the most likely to be acted upon, but in contrast delusions of guilt or catastrophe appeared to decrease the chance of delusional behaviour. Actions associated with abnormal beliefs are more common than has been suggested.