Recent proposals concerning the relationship between thematic structure and syntactic structure, including the idea of thematic hierarchy, when used with certain language-specific properties, offer insight into some problems concerning the Mandarin Chinese phrase structure condition (PSC). The PSC is such that the internal structure of XP contains at most one sub-phrase that is head-initial and lexically branching. Proposed originally as a surface structure filter in Mandarin, the PSC has various conceptual and empirical problems. By rethinking the data covered by the PSC with the help of syntactic and thematic structure theory, the new underlying structures for sentences that violate the PSC make the condition largely irrelevant as a surface filter. Independent reasons are sought for the poor formation of a number of sentences and counter-examples to the original PSC. (Contains 20 references.) (MSE)