The clinical approach to adults with congenital heart diseases (ACHDs) is unique in cardiovascular medicine because these patients encompass a broad range of presentations. Each patient, despite having similar diagnosis, will be anatomically and physiologically unlike others within ACHD population, in relation to the type of repair, age at repair, associated defects, with specific long-term risk factors and complications. Furthermore, as many patients will not complain of symptoms, clinical evaluation and diagnostic testing must also be based on the underlying main diagnostic category, with complete standardized lesion-specific clinical protocols, investigating all known risk factors specific for each congenital heart disease and performed as part of screening for significant long-term complications. The first part of this review will focus on clinical history, physical examination, and the most important diagnostic testing in ACHD population. The second part of the article will focus on some clinical issues we have to face in our daily practice, such as heart failure, cyanosis, and pulmonary hypertension. Furthermore, as survival rates of ACHD population continue to improve and patients with this condition live longer, we will briefly report on a new clinical concern regarding the impact of acquired morbidities like coronary artery disease that appear to be of greater importance in defining outcome in older patients with ACHD.