Sixty-eight patients with isolated valvular pulmonic stenosis with intact ventricular septum diagnosed by cardiac catheterization underwent a repeat study one to twelve years later which documented the progression of the lesion. These 68 patients were classified into two groups according to age. Group I comprised 37 patients who were less than one year of age at the initial study, and Group II comprised 31 patients who were older than one year of age at the time of the initial study. These 68 patients were divided into three groups according to their systolic right ventricular pressure and classified as mild, moderate, or severe. Increasing severity of the lesion was noted much more frequently in Group I, even with patients who were noted to have mild stenosis at initial cardiac catheterization. This was not as marked in Group II. The incidence of patent foramen ovale was noted to be much higher in Group I as compared with Group II. A much greater number of patients required surgery after repeat cardiac catheterization in Group I as compared with Group II. Our data indicate that mild cases of pulmonic stenosis in Group I can become severe at a later date, whereas this was less likely in Group II. Those with moderate and severe stenosis can remain the same or become more severe as age advances in both groups.