The invention relates to the fitness check of value documents. For at least two fitness criteria there is respectively determined with the aid of an unfit function an unfit degree of the particular value document. The unfit function clearly assigns an unfit degree to the fitness measurement values and has two threshold values, beyond which the unfit degree with respect to the relevant fitness criterion is 0 or 1. Between the threshold values there is an uncertainty range in which the unfit degree is, with respect to the relevant fitness criterion, between 0 and 1 and the unfit function behaves monotonously dropping or monotonously rising. Subsequently, the unfit degrees of different fitness criteria are combined into an unfit probability of the particular value document and on the basis of the unfit probability a fitness classification of the particular value document is carried out.