There is an increasing national trend toward initial venovenous (VV) extracorporeal membrane oxygenation (ECMO) for infants and children with respiratory disease; however, some proportion of patients initiated on VV ECMO will ultimately require conversion to venoarterial (VA) support for circulatory augmentation. The purpose of this work is to describe patients who required conversion from VV to VA ECMO and to highlight the increased mortality in this population. Demographic and disease-specific data on children who underwent VV-to-VA ECMO conversion were extracted from the Extracorporeal Life Support Organization registry. Survival comparisons to age-matched patients undergoing unconverted ECMO runs were made using the 2016 Extracorporeal Life Support Organization International Summary report. The relative risk (RR) of death associated with VV-to-VA conversion was calculated, and statistical analysis of survival was performed using a chi-squared test with P < 0.05 for significance. This study cohort consisted of 1382 patients who required VV-to-VA conversion. The overall hospital survival rate for neonates requiring conversion was 60%, compared with 83% for unconverted VV runs and 64% for unconverted VA runs (RR 1.23; 95% confidence interval, 1.14-1.34). Similarly, the survival of older children requiring conversion was 46% compared with 66% and 51%, respectively (RR 1.16; 95% confidence interval, 1.06-1.27). VV-to-VA conversion does occur and is associated with increased mortality. The need for conversion from VV to VA ECMO may represent an early failure to recognize physiologic parameters or disease severity that would be better managed with initial VA support. Further research is needed to pinpoint the cause of increased mortality and to identify predictors of VV failure to optimize initial mode selection.