Recent years have seen a growing literature on ex post assessment of merger cases, primarily evaluating the "correctness" of specific merger decisions by competition authorities. The question whether notifications regimes are efficient, i.e. whether competition authorities are in a position to review the set of mergers that potentially raises competitive concerns, has however largely been neglected so far. This paper attempts to fill this gap by evaluating the effectiveness of the Swiss merger notification regime. In particular, the focus lies on the level of turnover thresholds which trigger notification duties.