In recent research on cross-linguistic differences in linguistic rhythm, it has been hypothesized that the traditional dichotomy ‘stress-timed’ versus ‘syllable-timed’ might be recast with respect to which level of the Prosodic Hierarchy constitutes the most prominent domain for the organization of prosodic structure. In this paper, we test the prediction that ‘stress-timed’ languages are characterized by a dominance of the prosodic word against a typological sample of 58 languages. Although there is a slight cross-linguistic tendency in favor of the prediction, there is no statistical support for the proposed correlation. Since counterexamples include not only individual languages but also entire language families, we advocate a different view on prosodic word domain structure. The prosodic word profile of a given language is more reliably predicted by the family membership of that language than by universal correlations concerning its rhythm class membership. We substantiate this claim by a survey of Mon-Khmer’s family signature on prosodic word domain structure in Mon, where sound patterns target either the monosyllabic stem or the maximally inflected disyllabic word.