In patients with transposition of the great arteries with intact ventricular septum (TGA-IVS), late presentation for surgical treatment is not uncommon. Earlier experience suggested an excess mortality for the primary arterial switch operation (ASO) when performed after the third week of life in such patients. The true age limit for the primary ASO, however, remains speculative. A best evidence topic was written to determine the safety of extending the age limit of the primary ASO for TGA-IVS beyond three weeks of age. Eight of 74 relevant papers constituted the best evidence to address the issue. Sufficient level II evidence was found to suggest that in experienced institutions in the current era, the ASO for TGA-IVS may be performed primarily in infants three to eight weeks of age with comparable early outcomes to younger patients. Kang et al. investigated 275 neonates (younger than 21 days) and 105 infants (age range 21-185 days) undergoing the primary ASO for TGA-IVS. They found no significant difference in terms of in-hospital mortality (5.5% vs. 3.8%) or need for mechanical left ventricular (LV) support (3.6% vs. 5.7%) between the younger and older groups, respectively. Of the younger group, 3.8% developed postoperative LV failure leading to death or mechanical LV support. All nine patients older than two months (age range 61-185 days) survived to discharge although two (aged 69 and 86 days) required mechanical LV support for postoperative LV failure. The postoperative course of the late ASO group, however, was significantly prolonged as reflected in the duration of postoperative ventilation (4.9 vs. 7.1 days, P=0.012) and length of postoperative stay (12.5 vs. 18.9 days, P=0.001). In the report of Sarris et al., 52 patients with TGA-IVS who were older than four weeks of age (36 were older than eight weeks) underwent a primary ASO with early mortality comparable with younger patients (2% vs. 3%, respectively). For infants between the ages of two and six months, the strength of the evidence favoring this management approach is limited by the small sample size of reported series and the increased requirement for mechanical circulatory support for postoperative LV failure.