The aim of this study was to develop and test the psychometric properties of the Croatian paper-and-pencil and Internet versions of the Career Decision-Making Difficulties Questionnaire (CDDQ). The CDDQ is based on the theoretical taxonomy of difficulties in career decision-making and comprises three major clusters of difficulties: Lack of readiness, lack of information, and inconsistent information that are further divided into 10 specific types of difficulties. The paper-and-pencil version and the Internet version were filled out by 451 and 568 high school students, respectively. Both versions of the Croatian CDDQ showed to be reliable and structurally equivalent measures. A hierarchical cluster analysis and confirmatory factor analysis generally supported the three-cluster classification system of career decision-making difficulties, with the exception of the Dysfunctional Beliefs Scale that was not significantly associated with any of the other scales. The associations between the CDDQ Scales on the one hand, and two measures of career maturity—Student Career Construction Inventory and Career Decision-Making Self-Efficacy Scale—were moderate and negative and thus supported the concurrent validity of the CDDQ. The results suggest revising the dysfunctional beliefs subscale or using the CDDQ without this scale in counseling practice.