Objective To explore the effect of polycythemia on retinopathy of prematurity (ROP). Methods The clinical data of 262 premature cases was analyzed retrospectively in Xi'an Children Hospital from January 2005 to January 2009. Polycythemia was found in 46 cases (17.56%), including 27 males and 19 females. In 216 infants without polycythemia (82.46%), 155 were male and 61 were female. The difference of the birth weight (t=0.730, P=0.466), gestational age (t=1.603,P=0.110), oxygen inhalation numbers (chi;2=0.04,P＞0.90) and times (t=1.225,P=0.223), and concentration (t=1.823,P=0.071) between polycythemia group and no polycythemia group were not significant. In order to diagnose ROP, the ocular fundus of all premature infants was examined with binocular indirect ophthalmoscope,and the stage of ROP was assessed.Results In all the premature infants,ROP was found in 120 cases (45.80%). In 46 cases of polycythemia, ROP was found in 25 cases (54.34%); in 216 infants without polycythemia, ROP was found in 95 cases (43.98%); the difference of ROP incidence between the two groups was not significant (chi;2=1.64, Pgt;0.1).In 120 ROP patients, 104 cases (86.67%) with ROP＜3 stage and 16 cases (13.33%) with ROP ge;3 stage were found. In 25 ROP patients with polycythemia, 18 cases (72.00%) with ROP ＜3 stage and 7 cases (28.00%) with ROP ge;3 stage were found. In 95 ROP patients without polycythemia, 86 cases (90.53%) with ROP ＜3 stage and 9 cases (9.47%) with ROP ge;3 stage were found. The difference of the incidence of ROP ＜and ge;3 stage between the two group was significant (chi;2=4.38, Plt;0.05). In 120 cases of ROP, prethreshold retinopathy was found in 106 cases (88.33%), while threshold and post-threshold retinopathy was in 14 cases (11.67%). In 25 ROP patients with polycythemia, prethreshold retinopathy was found in 19 cases (76.00%), and threshold and post-threshold retinopathy was in 6 cases (24.00%).In 95 ROP infants without polycythemia, pre-threshold retinopathy was found in 87 cases (91.58%),while threshold and post threshold retinopathy was in 8 cases (8.42%).The difference of the incidence of ROP with prethreshold, and threshold and post-threshold retinopathy between the two groups was not significant (chi;2=3.27,P＞0.05).Conclusion Polycythemia may not affect the incidence of ROP,but impact on the severity of ROP.