Abstract: A device for determining the position of objects (T) inside a space (P), in particular for locating a tumor inside a human body. At least one emitter unit (SE) and at least one receiver unit (S11, . . . S22) are provided and, in a first embodiment, the emitter unit(s) (SE) are located inside and/or as close as possible to the object (T) under observation and the receiver units(s) (S11, . . . S22) are located preferably outside the space (P). In a second embodiment, the receiver unit(s) (SE) are located inside and/or as close as possible to the object (T) under observation and the emitter unit(s) (S11, . . . S22) are located preferably outside the space (P).