To determine the spontaneous progression of valvular aortic stenosis and to delineate clinical factors related to progression, a longitudinal study, including 49 patients (aged 16 to 81 years), was performed. All patients had auscultatory findings of aortic stenosis and multiple Doppler echocardiograms separated by at least 11 months. Rapid progression of aortic stenosis was defined as an increase of maximal instantaneous pressure gradient by greater-than-or-equal-to 10 mm Hg per year. During a mean follow-up period of 32 months (11 to 66 months), maximal pressure gradient rose from 38 +/- 15 to 60 +/- 20 mm Hg in the entire study population, resulting in a median increase of 7.2 mm Hg per year. In 21 patients (43 percent), an increase of greater-than-or-equal-to 10 mm Hg per year was found; in this subgroup with rapid progression, patients were older (64 vs 53 years, p < 0.01) and coronary artery disease was more prevalent (38 percent vs 7 percent, p = 0.01). We conclude that nearly half the patients with initially mild to moderate valvular aortic stenosis reveal a progression of greater-than-or-equal-to 10 mm Hg per year.