BACKGROUND: The majority of patients with congenital heart disease (CHD), nowadays, survives into adulthood and is faced with long-term complications. We aimed to study the basic demographic and clinical characteristics of adult patients with congenital heart disease (ACHD) in Greece.METHODS: A registry named CHALLENGE (Adult Congenital Heart Disease Registry. A registry from Hellenic Cardiology Society) was initiated in January 2012. Patients with structural CHD older than 16years old were enrolled by 16 specialized centers nationwide.RESULTS: Out of a population of 2115 patients with ACHD, who have been registered, (mean age 38years (SD 16), 52% women), 47% were classified as suffering from mild, 37% from moderate and 15% from severe ACHD. Atrial septal defect (ASD) was the most prevalent diagnosis (33%). The vast majority of ACHD patients (92%) was asymptomatic or mildly symptomatic (NYHA class I/II). The most symptomatic patients were suffering from an ASD, most often the elderly or those under targeted therapy for pulmonary arterial hypertension. Elderly patients (>60years old) accounted for 12% of the ACHD population. Half of patients had undergone at least one open-heart surgery, while 39% were under cardiac medications (15% under antiarrhythmic drugs, 16% under anticoagulants, 16% under medications for heart failure and 4% under targeted therapy for pulmonary arterial hypertension).CONCLUSIONS: ACHD patients are an emerging patient population and national prospective registries such as CHALLENGE are of unique importance in order to identify the ongoing needs of these patients and match them with the appropriate resource allocation.