Bladder pressure in the storage phase is considered to be relevant to the changes in the upper urinary tract. We analyzed retrospectively detrusor hyperreflexia, vesical compliance and maximum urethral closing pressure to determine which is the most significant factor relevant to the incidence of vesicoureteral reflux in 91 myelodysplastic patients. Vesicoureteral reflux was demonstrated in 29 of 91 patients. Cystometry and urethral pressure profilometry were performed in 69 and 27 patients, respectively. Vesicoureteral reflux was observed in 43% of the female patients, which was significantly greater than in the male patients (20%). Detrusor hyperreflexia was noted in 43 patients. Average vesical compliance was 11.3 ± 8.3ml./cm. water in 58 evaluable patients. Maximum urethral closing pressure was 56.7 ± 25.8cm. water. Vesical compliance in the patients with vesicoureteral reflux was 10.2 ± 7.5, which was not significantly lower than in those without vesicoureteral reflux (12.2 ± 8.8). The incidences of vesicoureteral reflux were 38% in the patients with vesical compliance of less than 10, 40% in those with vesical compliance of greater than 10 but less than 20 and 36% in those with vesical compliance of more than 20. The differences were not significant among these patients. Urethral pressure in the patients with vesicoureteral reflux was significantly higher than in those without vesicoureteral reflux (73.8 ± 23.5 versus 48.2 ± 23.0, p <0.05). The incidence of vesicoureteral reflux was 53% in the patients with urethral pressure of greater than 50, while it was only 8%, significantly less (p <0.05), in the lower urethral pressure group. Vesicoureteral reflux was noted in 44% of the patients with detrusor hyperreflexia, which was not significantly greater compared to 31% in the patients without detrusor hyperreflexia. These results suggest that in myelodysplastic patients maximum urethral closing pressure is highly relevant to the incidence of vesicoureteral reflux, while vesical compliance and detrusor hyperreflexia are not. The incidence of vesicoureteral reflux was significantly greater in female patients (43%, p <0.05) than in male patients (20%), although urethral pressure values showed no difference between them, indicating that female patients may be another risk factor for vesicoureteral reflux.