Vaso-occlusive painful crisis is one of the characteristic manifestations of sickle cell disease (SCD). We aimed to investigate the state of renal vascular resistance by means of Doppler ultrasonography during vaso-occlusive painful crisis in patients with SCD. The 60 patients with homozygous SCD who entered the study were divided into 2 groups. Group I included 45 patients who were living in steady-state conditions and had no history of transfusions within the 3 months before the initiation of the study. Group 2 consisted of 15 patients with signs of painful vaso-occlusive crisis during evaluation. Group 2 patients had significant reductions in 3 measures of flow velocity in both main renal arteries, compared with group 1 patients (P < .04, P < .001, and P < .01). Mean and end-diastolic velocities in the segmental arteries (P < .01, and P < .001, respectively) and end-diastolic velocities in the interlobar arteries (P < .04) were lower in group 2 patients than in group 1 patients. Analysis of resistive (RI) and pulsatile (PI) indices in the investigated arteries demonstrated that the RI of the renal (P < .001; P < .0001.), segmental (P < .002; P < .0001) and interlobar (P < .001; P < .0001) arteries of both kidneys in group 2 patients were significantly higher than the RI in group 1. patients and the control subjects, respectively. Total PI (P < .003; P < .0001) and total RI (P < .0001; P < .0001) for both kidneys were markedly higher in group 2 patients than in group 1 patients and the healthy subjects, respectively. Our preliminary results suggest a reduction of renal blood flow and an increase in renal vascular resistance during painful crisis compared with steady-state SCD.