There is a broad consensus in the literature that vowel-specific formant patterns differ as a function of gender (men/women) or age (adults/children) due to different average vocal tract sizes. Although an additional influence of fundamental frequency F0 is discussed in corresponding normalization approaches, formant patterns relating to sounds of adults and children that exhibit the same F0, to sounds of adults with higher F0 than sounds of children, and to sounds of men with higher F0 than sounds of women are barely compared. Investigating vowels of men, women, and children producing sounds with varying F0, we observed (1) a possible decrease or even a disappearance of the expected speaker-group differences in the formant frequencies < 1.5 kHz if F0 of the utterances correspond for children, women, and men, and (2) a possible “inversion“ of the expected speaker-group differences < 1.5 kHz if F0 of the utterances of adults are higher than those of children, or F0 of men are higher than those of women. However, no corresponding relationship between F0 and the higher formants > 1.5 kHz was found. These observations call for a further examination of the role of F0 when interpreting speaker-group related differences in formant patterns.