Unhealthy eating is associated with various diseases, such as cardiovascular, neurodegenerative, or oncological. There are neither economical nor behavior-related questionnaires available in the German language to assess general dietary behavior. Therefore, the aim of this validation study was to develop an instrument considering these aspects and verifying its construct and criterion validity. The new questionnaire is based on the general nutrition recommendations of the World Health Organization and the German Nutrition Society. It consists of 16 items that contrast dietary behaviors on a semantic differential scale. Our German-speaking convenience sample consisted of 428 participants. The construct validity of the General Dietary Behavior Inventory (GDBI) could be confirmed by examining convergent and discriminant validity. Furthermore, criterion validity was confirmed (significant negative correlations with body weight, Body Mass Index, and positive correlations with physical/mental health as well as life satisfaction). A cluster analysis revealed two different dietary behavior clusters representing a rather healthy and a rather unhealthy dietary behavior cluster. The results indicate that the GDBI is a validated and economical instrument to assess general dietary behavior. In practical research, this questionnaire helps to assess dietary behavior and to derive interventions for a healthy dietary behavior in concordance with international nutrition recommendations.