A new medical community, the grown-up congenital heart patients--GUCH--has resulted from successes of cardiac surgery over 30-40 years. Many survivors have complicated problems, medical and surgical, demanding experience and expertise neither provided nor organised in most countries. Islands of good care exist with difficulty. The experience of one specialist GUCH unit established for 25 years shows that 55-60% admissions are for complex lesions, particularly after complicated surgery. The patients' overall costs are at least twice those of other cardiac patients. GUCH admissions are about 5-8% of the total, varying according to the population/region served. Supervised medical care for GUCH is equally important in outpatient services, involving 3 times the secretarial time of other cardiac patients, an accessible database and a "helpline" for doctors and patients. This may be life-saving in patients with complex conditions. The GUCH population is ageing, with increasing numbers of complex patients. 30% of admissions now are over 40 years old, and 5% are over 60, confirming that this is an adult medical speciality, not paediatric. Invasive investigations and arrhythmias provide the most frequent reasons for admissions--atrial flutter is the commonest arrhythmia, needing experts when it occurs in Fontan, transposition, etc. Routine coronary arteriography is also important. In cardiac surgery, one in five admissions presents organisational problems. Reoperation, now as many as 9 or 10 times, has to be optimised. Reoperation on left and right outflow tracts-for changing valves and conduits--is more common than first operations. GUCH patients represent a relatively small portion of the whole population. Such patients in a population of 7-8 million need to be concentrated in 1-2 centres, depending on culture, religion, geography, language etc., to provide necessary experience, expertise and education.