This paper argues that the simple reflexive pronoun sig is unambiguously a thematic argument in Icelandic. This is shown to be true not only of sig with naturally reflexive verbs but also of inherently reflexive sig. This view is mainly supported by two sets of facts:(i) that sig is impossible with verbs that fail to theta-mark their object (middles and anticausatives), and (ii) that case assignment works the same way for sig as for non-reflexive DP arguments. Potential counterarguments against my view involving focalization and reflexive passives are argued not to be valid.