Good correlation between Doppler-derived and catheterization-measured pulmonary valvar pressure gradients has previously been reported. The purpose of this paper was to present two groups of patients who did not show such correlation, namely those with very severe stenosis and those measured immediately following balloon pulmonary valvoplasty. Twenty-two patients, aged 4 months to 20 years, in whom Doppler and catheterization pressure gradients were measured within 24 hours of each other were included in the study. There were 35 pairs of such data. The correlation coefficient for the entire group was 0.61 which improved to 0.91 when the five patients with severe stenosis (gradients of 94 to 190 mm Hg) and one patient with severe right ventricular infundibular stenosis immediately following balloon valvoplasty were excluded from analysis. Although the possibility exists, technical aspects of Doppler recording did not appear to be causing this lack of correlation. Cone-shaped spray formation rather than a focused jet in patients with extremely severe pulmonary stenosis may be postulated to be responsible for poor prediction by Doppler of catheterization gradient. Once these two groups of patients are excluded, there is excellent correlation between Doppler and catheterization gradients in patients with pulmonic stenosis.