The aim of our study was to establish the extent to which therapy of hypertrophic obstructive cardiomyopathy (HOCM) can influence the degree of hypertrophy. By means of two-dimensionally guided M-mode echocardiography, 120 patients with HOCM (age range 4–72 years, mean age 41 years) were observed over an average period of 49 ± 41 months. Depending on the respective therapy, we formed four patient groups: group 1:13 patients without any therapy (follow-up period 31 ± 30 months); group 2: 27 patients receiving propranolol (follow-up period 47 ± 34 months); group 3: 50 patients receiving verapamil (follow-up period 39 ± 27 months), and group 4: 30 patients with myectomy (follow-up period 34 ± 32 months). In group 4, as expected, the thickness of the interventricular septum (IVS) decreased postoperatively (from 24.2 ± 4.5 to 19.8 ± 6.7 mm, p < 0.05), and the left ventricular posterior wall (LVPW) thickness also decreased later postoperatively (from 13.0 ± 2.6 to 11.9 ± 2.3 mm, p < 0.05). The left ventricular diameters increased. In groups 2 and 3 treated with pharmacotherapy as in the untreated patients of group 1 on average there was no change in IVS and LVPW thickness nor in the left ventricular diameters (with the exception of increasing left ventricular end-diastolic diameter in the propranolol-treated group). In contrast to group 1 in occasional cases there were substantial decreases of IVS thickness (11% of the patients in group 2, 13 % in group 3) or LVPW thickness (13% of the patients in group 2, 12% in group 3). However, the thickness remained mainly unchanged (IVS: 74% of the patients in group 2, 71% in group 3; LVPW: 67% in group 2, 70% in group 3) or increased (IVS: 15% in group 2, 17% in group 3; LVPW: 21 % in group 2, 19% in group 3). The differences between groups 2 and 3 were not significant. Thus, our investigations indicated that on average neither propranolol nor verapamil leads to a regression of hypertrophy in HOCM.