The phenomenon of intrinsic vowel F0 (IF0), in which high vowels exhibit higher F0 than low vowels, has been widely attested in languages of the world. Most often, IF0 is regarded as an automatic, physiologically determined phenomenon, whereas some claim that IF0 is a controlled feature, introduced to enhance vowel contrasts. This paper presents new evidence on this issue by means of a cross-linguistic investigation of the influence of vowel inventory size on IF0 and a study of IF0 in second language (L2) acquisition. IF0 was measured in three language varieties: Arabic (a language with 3 vowels), Dutch (a 12-vowel system), and Dutch spoken by native Arabic-speaking learners. IF0 was significantly larger in Dutch than Arabic, but did not differ significantly between Arabic and Dutch produced by L2 learners. No spectral differences between the corresponding vowels of the three language varieties were found. While confirming the universality of IF0, these results also suggest that the size of IF0 may be language-specific, depending on the need to enhance vowel contrasts. Thus, these results agree well with a mixed physiological-enhancement account, which assumes that IF0 is physiologically determined, but also at least in part the effect of an interacting, controlled mechanism.