A positioning device for keeping a monitoring device for tyres of vehicle wheels in an installation condition, includes: two separate active portions, each having a main surface the shape of which matches that of a respective portion of an outer surface of a monitoring device, said separate active portions being adapted to cooperate with at least base portions of said monitoring device so that, when said positioning device is associated with said monitoring device, the base portions of said monitoring device are maintained at a given mutual distance by said active portions.