168 patients with fixed subaortic stenosis (fixed SAS) were studied between 1959 and 1987. For assessment of the long term prognosis, the hemodynamic results of the catheterizations were compared with the angiograms. The obstructive lesions were divided into 4 basic types: 1) thin fibrous ridge subjacent to the valve, 2) funnel shaped, 3) irregular fibromuscular, 4) tunnel shaped. Operative reports were used in all and 2D-echocardiography in so far 67 patients to distinguish between pure fibrous and fibromuscular types. The average age at initial diagnosis was 7.8 years (5 weeks to 23 years). Only 4 of 168 patients had significant obstruction in early infancy. All 4 had Shone's complex. Progression of the disease was documented in 30 of 34 patients (80%) by serial catheterization; regrowth was noted in only 4. In 10 patients fixed SAS was not detected by the 1st catheterization but was present subsequently. 22 patients had additional dynamic obstruction, proved in 19 during the second decade of life. Among 132 operated patients, there were 11 early (8%) and 3 late (2%) deaths. Twenty underwent reoperation for residual obstruction. The mean postoperative gradient across the left ventricular (LV) outflow tract of 89 patients recatheterized after conventional operation was as follows: Type (1) 16 +/- 17, (2) 19 +/- 16, (3) 51 +/- 41, and type (4) 79 +/- 24 mmHg. Complete assessment confirmed that only 33% of the operations led to satisfactory hemodynamic results. Our data show that the pure fibrous forms have a better prognosis than the fibromuscular forms and are better differentiated by 2D-echocardiography than by angiography.(ABSTRACT TRUNCATED AT 250 WORDS)