Among one hundred and five consecutive patients with pre-excitation (PE) syndrome studied during a 10-year period, eight had an associated hypertrophic cardiomyopathy (HC) (7.62 per cent), eight had a coronary heart disease (7.62 per cent) and nine had a hypertensive heart disease (8.57 per cent). Of the eight patients with HC, four had an asymmetrical form (three of them with an obstructive component), and four a symmetrical form. Seven of these patients had a Wolff-Parkinson-White (WPW) type of PE and the remainder a Lown-Ganong-Levine type of PE. The incidence of paroxysmal tachycardias in the total group was 56.2% (61/105) and in the patients with associated HC was 62.5% (5/8). One of these latter patients had a concomitant brady-tachy syndrome and a severe obstructive form of HC. He was surgically treated (septal myomectomy and section of accessory atrioventricular pathway). The ECGs and VCGs of the seven patients with the HC-WPW type of PE association showed the coexistence of incomplete left bundle branch block of left ventricular hypertrophy patterns. The eight patients with associated HC were closely followed up from two to seven years (total follow-up period 435 patient/months). One of them died suddenly during the 40th month of follow-up. This study suggests that: 1) HC-PE association is not infrequent; 2) the incidence of paroxysmal tachycardias in the subgroup is quite similar to that presented in isolated PE; and 3) the electrocardiographic and vectorcardiographic changes in the HC-WPW type of PE association are highly specific.