Endothelin‐1 (Et‐1) is a vasoconstrictor produced by endothelial and vascular smooth muscle cells in response to hypoxia, which induces hypertrophy in cultured cardiac myocytes. We measured plasma Et‐1 levels and left ventricular dimensions in 13 patients with sickle cell anemia (SCD) and in 12 African‐American controls ages 16–29 years. Endothelin‐1 concentrations are significantly higher in SCD subjects than controls (10.6 + 1.9 vs. 3.0 + 1.3 pmol/L). There was a negative correlation between oxygen saturation and Et‐1 levels in SCD patients (r = ‐0.71, P = 0.01). SCD subjects have more dilated and hypertrophied hearts corrected for body surface area than controls as evidenced by significant increases in left ventricular end diastolic dimension (31 + 0.8 vs. 24 + 0.9 mm/m², P < 0.001), left ventricular end systolic dimension (20 + 0.9 vs. 16 &plus 0.8 mm/m², P = 0.002), left ventricular posterior wall thickness (5.0 &plus 0.1 vs. 4.0 &plus 0.1 mm/m², P < 0.001), and left ventricular mass (125 + 7.2 vs. 69 + 5.1 g/m², P < 0.001). The index of left ventricular function, the shortening fraction, was not different between groups (34 + 1.2% in SCD vs. 35 + 1.5% in controls). The correlation between left ventricular mass and levels of Et‐1 in SCD subjects was not significant (r = 0.47, P = 0.121). Am. J. Hematol. 58:195–199, 1998. © 1998 Wiley‐Liss, Inc.