OBJECTIVE: To determine whether the rate of feed advancement affects the incidence of necrotizing enterocolitis (NEC). STUDY DESIGN: Prospective randomized controlled trial involving 185 formula-fed infants with birth weight 501 to 1500 g and gestational age =34 weeks. Infants were randomized into 2 groups: "slow" (n = 98), who received 15 cc/kg/d increments (a 10-day schedule to full feeds) and "fast" (n = 87), who received 35 cc/kg/d increments (a 5-day schedule to full feeds) of Similac Special Care 20 cal/oz. Feeds were increased only if well tolerated as defined by a protocol. RESULTS: The incidence of NEC (Bell stage >/=II) was similar in both groups (slow 13% and fast 9%, P =.5). The incidence of perforation (Bell stage III) was also similar in both groups (slow 4% and fast 2%, P =.8). Feeds were started at a comparable postnatal age in both groups (median age: slow 5 days and fast 4 days, P =.9). Although the neonates in the fast group attained full enteral intake earlier (median days [25th and 75th percentiles]: slow 15 [12, 21] and fast 11 [8, 15], P <.001) and regained their birth weight earlier (slow 15 [11, 20] and fast 12 [8, 15], P <.05), their ages at discharge were not statistically different (slow 47 [31, 67] and fast 43 [29, 62], P =.3) CONCLUSIONS: A greater than twofold difference in the rate of feed advancement from 15 cc/kg/d to 35 cc/kg/d did not affect the incidence of NEC >/= stage II. Factors other than feed advancement appear to be more important in the pathogenesis or progression of NEC.