This investigation was undertaken to determine whether a relation could be identified between left ventricular wall thickness and age in a large population of symptomatic patients with hypertrophic cardiomyopathy. Extent of left ventricular hypertrophy was assessed with two-dimensional echocardiography in 173 patients with hypertrophic cardiomyopathy who ranged in age from 21 to 74 years (mean 45) and had mild to severe cardiac symptoms. The overall study group was classified into five age subgroups (each corresponding to a decade); maximal left ventricular wall thickness and wall thickness index (a quantitative expression of the overall extent of hypertrophy) were assessed in each group. These two indexes were significantly higher in patients 21 to 30 years of age than in patients in each of the other four older age groups. The two indexes of left ventricular hypertrophy were also significantly higher in patients 31 to 40 years of age than in patients who were 61 to 74 years old. Multivariate regression analysis showed that the relation between wall thickness and age was not influenced by other clinical variables such as severity of symptoms, presence of subaortic obstruction, left ventricular cavity dimension and gender. In conclusion, the findings indicate that, in a population of symptomatic adult patients with hypertrophic cardiomyopathy, left ventricular hypertrophy is considerably more severe in younger than in older patients and that there is an inverse relation between left ventricular wall thickness and age.