Glottal flow waveforms estimated by inverse filtering acoustic speech pressure signals were compared to glottal area functions obtained by digital high-speed imaging of the vocal fold vibration. Speech data consisted of breathy, normal and pressed phonations produced by two male and one female subjects. The results yield both qualitative and quantitative information about the relationship between the glottal flow and the corresponding area function. It was shown, for example, that a distinct knee in the glottal flow waveform in the opening phase corresponds to the abrupt opening of the vocal folds in normal and pressed phonation. In addition, the obtained quantitative data corroborates known theoretical considerations according to which the shape of the glottal flow is more asymmetric than the corresponding area function.