Hypertrophic cardiomyopathy is an autosomal dominant disease characterized by asymmetrical left ventricular hypertrophy, myocyte disarray, interstitial fibrosis, and small vessel disease. More than 100 mutations in 10 genes, all encoding for sarcomeric proteins, have been identified as responsible for this disease. While the etiology of hypertrophic cardiomyopathy has been extensively elucidated, its pathogenesis is not completely understood. Mutated proteins are incorporated in the sarcomere and impair myocyte contractility. This probably triggers the compensatory local release of trophic factors, which influence the development of the typical anatomical features of the disease. Modifying genes or the effect of environmental or local factors is likely to play a role. Interstitial fibrosis is a morphological characteristic of hypertrophic cardiomyopathy and, increasing chamber stiffness, is an important determinant of diastolic dysfunction. Studies on transgenic animals with hypertrophic cardiomyopathy emphasize the role of interstitial fibrosis in this disease. Recently our group has shown that collagen turnover, evaluated through serum markers of collagen metabolism, is more active in patients with hypertrophic cardiomyopathy than in normal subjects and that patients with passive diastolic dysfunction accumulate collagen I. These studies are potentially relevant as they allow to assess the effects of therapy with cardioreparatory drugs.