Domain-Specific Modeling Languages (DSML) play a key role in model-driven development. There are many approaches how to create a DSML. Recent trends in domain-specific modeling languages and issues of creating and using UML profiles are discussed in this paper. Then we present a novel approach for defining a full-featured DSML based on a UML profile and its customization instead of heavyweight metamodeling. This approach was implemented in MagicDraw tool and already successfully accepted by its users. Also, MagicDraw developers themselves applied it for creating SysML, DoDAF and UPDM modeling environments. The main benefit of this approach is that it allows a DSML modeler to reuse powerful features of already existing tools. We propose a seven-step DSML development process and illustrate it by an example demonstrating creation of a DSML for modeling organization structures. We also discuss benefits of taking the presented approach and some ideas for future enhancements based on the feedback of users.