Polish is known for having two levels of stress – penultimate primary stress and iterative rhythmic stress on odd-numbered syllables, forming a typologically rare binary system with internal lapses. Rhythmic stress has been reported to be cued by increased onset consonant duration relative to unstressed positions, both word-initially and word-medially. Little is known about the potential role of consonant duration as a phonetic correlate of primary stress. Hitherto available acoustic studies, relying mostly on vocalic parameters, often point to a strong dependence of those parameters on the focus position. In this study, we report acoustic results of an experiment designed to measure onset consonant (as well as vocalic) duration across the syllables of segmentally matched three-and four-syllable words, e.g. telefon [010] ‘telephone (nom. sg.)’, telefon+y [2010] (nom. pl.); 0 = unstressed, 1 = primary stress, 2 = rhythmic stress. In order to disentangle the potential effects of sentence-level prominence, the stimuli appeared in discourse-new, contrastive focus, and no focus contexts. Our results demonstrate significantly increased onset consonant duration in primarily/rhythmically stressed syllables relative to unstressed syllables, occurring to a different degree both in the presence and absence of focus.