In a first section, the present thesis deals with the decision of the ECJ in the case C-453/10 (Perenicova and Perenic) which was rendered in March 2012 as well as with an in-depth analysis of the dispute in the main proceedings according to Austrian law. The paper, however, only addresses the first question referred for a preliminary ruling of the ECJ by the Okresny sud Presov as the referring court. This question deals with the interpretation of Council Directive 93/13/EEC of 5 April 1993 on unfair terms in consumer contracts. The referring court inquires to know whether the extent of the legal protection resulting from Art 6 paragraph 1 of the directive can be understood as to permitting to declare the whole contract void in case of usage of unfair terms in consumer contracts if that is more favourable for the consumer, rather than only a partial voidness of the contract. After a detailed discussion of the ECJ decision in this matter, its case is fictitiously transferred to Austria and it is reviewed in a case study how it would be judged according to Austrian law. Since the consumer credit contract in the present case includes an intransparent as well as usurious clause, the legal consequences resulting from this are vast. To start with, the legal consequences of the implementation of the transparency control of § 6 paragraph 3 KSchG on the present case are analysed. Subsequently, the paper addresses the question to what extent the incorrect designation of the effective interest rate represents a violation of § 9 VKrG on mandatory particulars in consumer credit contracts and how this is to be sanctioned. The thesis also deals with the problem of usury. In a final section the paper investigates whether the action of the creditor can be qualified as immoral and whether the contestation of the contract on the basis of absence of intent may be possible.