This essay examines the impact of the distinction between situations and cases under the Rome Statute in national laws on co-operation with the ICC. It argues that this distinction is likely to create difficulties in three areas: (i) the communication of the notitia criminis to the Court; (ii) admissibility issues in proceedings under Articles 18 and 19 of the Statute; and (iii) the efficacy at national level of admissibility rulings by the Court.