Background: We analysed the experience with hypertrophic cardiomyopathy in two paediatric centres to establish the differences from older patients. Methods: Out of 45 young patients seen from 1974 to 1999, we included 38. Criterions for exclusion were secondary forms, or association with severe congenital cardiac disease which could alter the outcome. Results: The patients presented at the age of 5.7 years, and were followed for 7.0 years. The 34 patients referred because of a murmur or cardiomegaly were older than the four with heart failure, presenting at 6.2 as opposed to 2.1 years of age, p = 0.08. Of the patients, 29 (76%) had primary cardiomyopathy, while 9 (24%) had secondary forms associated with Noonan's and LEOPARD syndromes. Familial tendency was ascertained in 7 patients (18%). The septal thickness in mm/m2 at presentation was greater in patients under 2 years than in older children (29 vs 18, p = 0.02). Obstructive hypertrophic cardiomyopathy was found in 17 patients (45%), with six of these having mild associated congenital cardiac defects. Nine had symptomatic arrhythmias. Overall, treatment was medical in 31, with DDD pacing used in 5, and surgery, radiofrequency ablation, and transplantation in one patient each. Total mortality was 24%, at a rate of 4.3% per year. Four patients died in heart failure and 5 had sudden death. Those in failure were significantly younger (p = 0.01). Conclusions: Hypertrophic cardiomyopathy in the young is characterized by referral for murmur or heart failure; frequent secondary forms; the obstructive variant being as common as the nonobstructive form; a mortality rate similar to that for adults attending tertiary centres; and less frequent familial forms than in older populations.