This article examines the grammatical behavior of Dutch adverbs featuring so-called adverbial -s. This will be done on the basis of three questions: Firstly, what is the grammatical nature of adverbial -s? Secondly, in which structural configurations does it appear? Thirdly, what does adverbial -s tell us about the existence of adverbs as a separate part of speech? The article provides the following three answers to these questions: Firstly, adverbial -s is an affixal manifestation of the categorizing heads n and a (so-called -s-Support). Secondly, n and a externalize as -s when the raised root that forms an amalgam with the categorizing head is silent or a bound root. Thirdly, “adverbs” featuring adverbial -s are nominal, adjectival or adpositional expressions with an articulated syntactic structure. Some of these syntactic structures correspond to the so-called construct state. In short, linguistic expressions featuring adverbial -s do not support the idea that adverbs form a separate part of speech.