Background: Adults with transposition of the great arteries (d-TGA) after the arterial switch operation (ASO) are an evolving cohort in adult cardiology. We aimed to analyze cardiac function and cardiac events after transition to the adult clinic in Switzerland. Materials and methods: Adults with prior ASO enrolled in the Swiss Adult Congenital HEart disease Registry (SACHER) were included. We analyzed initial cardiac anatomy, surgical history, residual lesions and cardiac function at the time of inclusion, as well as cardiac events during follow-up. Patients were classified as complex (with ventricular septal defect) or simple (with intact interventricular septum) d-TGA. Results: The cohort included 149 patients (99 simple d-TGA, 50 complex d-TGA; age 21±3 years; 71% male, follow-up 27 [15-46] months). Prior to inclusion, patients with complex d-TGA had undergone more interventions related to the left ventricular outflow tract (16% vs. 3%, p = 0.01). Functional and cardiovascular status were similar between the groups. Eleven patients (7%) had a total of 19 cardiac events (5 complications and 14 re-interventions) during follow-up. Patients with complex d-TGA had more cardiac-related complications compared to those with simple d-TGA (8% vs. 1%, p = 0.03). The frequency of re-interventions was not statistically different between the two groups (12% vs. 4%, p = 0.07). During follow-up, an increase in QRS duration was observed. Other parameters of cardiac function remained unchanged. Conclusion: The majority of adult ASO patients have normal functional class and cardiac function. Complex anatomy and residual lesions play a key role when regarding the occurrence of cardiac-related complications during follow-up. The role of QRS prolongation over time needs to be investigated further.