The new provisions on national parliaments in the Lisbon Treaty were welcomed with scepticism by some scholars and with hope by others. Sometime after the new provisions came into force, their impact on the role of national parliaments in the EU can already be examined. This article looks into the effect of the implementation of the Early Warning Mechanism and the other provisions on the parliamentary scrutiny of EU affairs in Spain. It also reflects on the possible implications for the EU political system. Although the scope and actual effect of the new measures have been quite modest, the new regulations allow for a better scrutiny of EU law, a tighter control of the executive on EU affairs and closer cooperation with EU institutions.