People use mental shortcuts to simplify the amount of information they receive from the environment. Heuristic reasoning can be included among these mental shortcuts. In general, heuristics is useful for making fast decisions and judgements, but in certain cases, it may lead to systematic errors because some relevant aspects presented in the given information are ignored. Heuristic reasoning is unconscious, that is, people are not aware of using it. The aim of this paper is to analyse in which ways these shortcuts affect the construction of judgement about immigration and ethnic diversity. For example, if the wrong strategy is chosen or some relevant information is ignored, we are likely to make decisions and judgements influenced by stereotypes and distorted images of reality (of immigration). (Contains 1 note and 4 tables.)