This paper presents the main features of a Multimedia Query Language tailored for content-based similarity retrieval of multimedia objects. The Query Language processor is a component of a multimedia database system that adopts a model that permits both a structural representation of raw multimedia data and an automatically computed description of the multimedia data content. The Query Language is an extension of a traditional object-oriented query language. It allows to express restrictions on features, concepts and structural aspects of the multimedia database objects. In addition, the language supports the formulation of queries with imprecise conditions. The outcome of a query execution is an ordered set of pairs, each one consisting of an object and a measure of the similarity of the object with the criteria specified in the query.