A factor model for midsagittal x rays of the Icelandic long and short vowels [i, I, e, y, ø, u, o, a] [M. Pétursson, Phonetics29(1–2), 22–79 (1974); M. Pétursson,Les Articulations de l'Islandais à la Lumière de la Radiocinématographie(Klincksieck, Paris, 1974)] was constructed. The factor model is based on single frames from the center of the vowels, and accounts for 95% of the variance in tongue positions with three factors. Sequences of x rays of the long and short diphthongs [ei, øi, ai, ou, au]including portions of the consonantal on‐ and off‐glides can be described by the same factors (>80% of the variance accounted for). We approximate the trajectories of the diphthongs by constructing curves that interpolate the measured positions in factor space. Examining the trajectory through factor space suggests an articulatory parametrization of diphthongs. [Work supported by NIH.]