The specific aim of this study is to evaluate the clinical effectiveness of inhaled nitric oxide (INO) for the treatment of acute vaso-occlusive pain crisis in pediatric patients with sickle cell disease. Nitric oxide (NO) deficiency is known to be central to the pathophysiology of vaso-occlusion. The aim is unchanged from the original application. The study is a randomized, double blind, placebo controlled, clinical trial with eligible patients randomized to receive either NO (with 21% O2 final concentration) for 16 hrs with 8 hr wean (80 ppm 0-8 hrs, 40 ppm 9-16 hrs, 20 ppm 17-20 hrs, 10 ppm 21-24 hrs) or placebo (21% O2 alone) for 24 hrs. The null hypothesis is that there is no difference in change in mean pain score after 16 hours between patients treated with NO and placebo. The primary outcome measure of the study remains the difference in mean change in pain scores between groups as assessed using a 10 cm visual analogue pain scale (VAS). Secondary outcome measures also remain the same. The study is a next step to our completed FDA Orphan Product Development Grant funded study (FD-R-001686) that evaluated safety and efficacy of NO used for 4 hrs for treatment of vaso-occlusive crisis in pediatric patients with sickle cell disease.