['Hypoplastic left heart syndrome (HLHS) is associated with significant mortality and morbidity. Fetal head growth abnormalities have been identified in a subset of HLHS fetuses, but it is unclear whether specific patterns of maladaptive growth affect clinical outcomes. We hypothesized that poor fetal head growth is associated with an increased frequency of adverse clinical outcomes.', 'We retrospectively examined a cohort of HLHS patients from midgestation to 1 y of age. Fetal and birth anthropometric measurements were analyzed using the Olsen standard, and clinical outcomes were obtained.', 'A total of 104 HLHS patients were identified over a 12-y period; fetal data were available in 38 cases. HLHS neonates demonstrated a high incidence of microcephaly (12%), small head size (27%), and poor head growth (32%). All-cause mortality was 31% at 30 d and 43% at 1 y. Neurologic outcomes were observed in 12% of patients and were significantly increased with microcephaly (43 vs. 4%; P = 0.02). The average length of hospital stay following stage I palliation was 33.4 ± 33 d, correcting for early death.'] Is microcephaly associated with early adverse neurologic outcomes in hypoplastic left heart syndrome?