Background: It is well established that the arterial switch operation is the surgical procedure of choice in patients with transposition of the great arteries and balanced ventricular anatomy. The surgical approach of choice in patients with transposition but unbalanced ventricular size is unknown. Objectives: Since the beginning of the arterial switch operation program, patients with transposition of the great arteries and unbalanced ventricles underwent biventricular repair by means of the arterial switch operation and repair of any associated lesions, either through a single or staged surgical procedure. The aim of this retrospective study is to analyze whether this approach can be proposed to such patients. Methods: Forty-four patients with transposition of the great arteries and unbalanced ventricles underwent this surgical approach since 1984. Two groups were defined: group I had transposition with a dominant right ventricle (n = 28), and group II had transposition with a dominant left ventricle (n = 16). In group I the median age and weight at the arterial switch operation were 8.5 days (range, 5-70 days) and 3.1 kg (range, 1.5-3.7 kg), respectively. The median end-diastolic left ventricular volume, mass, and long-axis ratio were 15 mL/m2 (range, 11- 16 mL/m2), 31.5 g/m2 (range, 20-66 g/m2), and 0.85 (range, 0.9-0.7), respectively. The mitral valve diameter was slightly hypoplastic, with a median z value of -1.22 (range, -0.3 to 3.7). In group 2 the median age and weight at the arterial switch operation were 42 days (range, 8 days-15 years) and 3.5 kg (range, 2.8-35 kg), respectively. Associated lesions in this group were coarctation in 9 and single (n = 12) or multiple (n = 4) ventricular septal defects. The median long-axis ratio and tricuspid z value were 0.6 (range, 0.3-0.8) and -0.9 (range, -0.5 to 3.3), respectively. In this group 9 patients had a single-stage procedure with fenestrated ventricular defect patches, atrial septal defect patches, or both: 7 patients underwent the staged approach. Results: In group I there was 1 early death from sepsis after weaning from postoperative extracorporeal membrane oxygenation. Three patients had severe pulmonary hypertension, one of whom died 1 year later. All survivors demonstrated, at discharge from the hospital, equilibrated ventricular size, with a median left ventricular end-diastolic volume of 25 mL/m2 (range, 21-30 mL/m2). In group II there were 2 early and 1 late deaths. All early deaths occurred in patients without voluntary residual intracardiac shunts. Median early postoperative long-axis ratio and tricuspid z value were 0.8 (range, 0.7- 1) and -0.2 (range, 0.74 to 1.2), respectively. Conclusion: This study demonstrates that the arterial switch operation in patients with transposition of the great arteries and unbalanced ventricles remains a good surgical option.