The paper answers one of fundamental questions for the Polish private international law (narrowly understood): is the principle of equal treatment all legal systems in this law illusion or reality? Achievement of the intended goal needed investigation of following issues, which related to this principle: genesis and theoretical basis, content and indications, deviations, domestic legislative tendency and views in domestic doctrine. Considerations included in the paper confirmed the existence of the principle of equal treatment all legal systems in the Polish private international law. However the realization of this principle is not fully satisfied and needs certain improvements.