We describe a new method for extracting Negative Polarity Item candidates (NPI candidates) from dependency-parsed German text corpora. Semi-automatic extraction of NPIs is a challenging task since NPIs do not have uniform categorical or other syntactic properties that could be used for detecting them; they occur as single words or as multi-word expressions of almost any syntactic category. Their defining property is of a semantic nature, they may only occur in the scope of negation and related semantic operators. In contrast to an earlier approach to NPI extraction from corpora, we specifically target multi-word expressions. Besides applying statistical methods to measure the co-occurrence of our candidate expressions with negative contexts, we also apply linguistic criteria in an attempt to determine to which degree they are idiomatic. Our method is evaluated by comparing the set of NPIs we found with the most comprehensive electronic list of German NPIs, which currently contains 165 entries. Our method retrieved 142 NPIs, 114 of which are new.