Elevated pulmonary artery pressures (PAP) occur in approximately 30% of children with sickle cell disease. In adults, pulmonary hypertension is significantly associated with mortality. There are no data on the long term significance in children. Nineteen children with SS/Sbeta(0) thalassaemia had elevated PAP, defined as tricuspid regurgitant jet velocity (TRV) > or =2.5 m/s on screening echocardiograms. They were prospectively followed for 23 months (range 19-31 months). Patients with initial TRV > or = 3 or TRV > or = 2.5 m/s on repeat echocardiogram had cardiopulmonary evaluation and were offered treatment with hydroxyurea. Associated conditions like asthma and obstructive sleep apnea were treated. 18/19 patients had follow-up echocardiograms. These showed normalization of TRV in 8 patients. Risk factors associated with persistent elevation were higher TRV on initial echocardiogram (P = 0.01), lower haemoglobin (P = 0.003) and lower oxygen saturation (P = 0.03). Five patients with persistently elevated PAP were treated with hydroxyurea. Mean right ventricular pressure dropped from 40.16 to 29.26 (P = 0.017) after 3-6 months and to 23.6 mmHg (P = 0.002) after 9-12 months on treatment. In conclusion (i) At borderline elevation of TRV there is intrapatient variability and echocardiograms should be repeated for confirmation. (ii) Elevated PAP are reversible in children with early detection and treatment with hydroxyurea.