Over a 21-month period 200 fetal echocardiographic studies were performed on pregnancies at high risk for congenital heart disease referred to the NSW Fetal Echocardiography Service. Four cases of hypoplastic left heart syndrome were diagnosed in-utero during this period. These cases demonstrated the heterogeneity of this lesion, its known association with other defects and chromosomal anomalies, and evidence of in-utero evolution. Hypoplastic left heart syndrome is reliably diagnosed by fetal echocardiography. This lesion is heterogenous and may evolve beyond the first trimester. Careful attention to ventricular function, endocardial echoes and Doppler flow may assist with diagnosis.