Abstract In Spanish lexical compounds, stress on the final constituent is consistently preserved; however, it is uncertain whether stress on the initial constituent is preserved as well. Some linguists claim that stress is deleted from the initial constituent, whereas a few argue, instead, that it is demoted from primary to secondary. Given that empirical evidence has been scarce, this issue remains unresolved. To inform the debate, the present study examines all known phonetic correlates of stress in both accented and unaccented contexts. The acoustic measures of lexical compounds are compared to those of non-compound words and phrases that have a similar segmental structure. The results demonstrate that the initial constituent of lexical compounds bears secondary stress. This secondary stress, as a result of stress demotion, differs from rhetorical secondary stress both phonetically and phonologically. These findings provide fresh insights into the definitional properties as well as the prosodic structure of Spanish compounds.