Two 21-day battery experiments were conducted with day-old broiler chicks fed a corn-soybean meal diet to re-evaluate the riboflavin requirement for optimum performance. In each experiment a total of 384 birds was assigned to six dietary treatments and given 0, 0.9, 2.0, 2.8, 3.6, or 4.4 mg of supplemental riboflavin/kg of feed. The corn-soybean meal diet was formulated to contain 22% CP and 3,200 kcal of ME/kg of feed. The analyzed riboflavin content of the unsupplemented diet was 2.6 mg/kg. A severe leg paralysis (inability to walk and to move one or both legs) was first observed between 10 to 12 days of age in birds receiving no supplemental riboflavin. Besides leg paralysis, high mortality and poor growth were the main signs of riboflavin deficiency observed. A minimum requirement for growth of 3.6 mg of riboflavin/kg of feed was determined using the broken-line technique. However, in order to prevent signs of leg paralysis, the minimum requirement of 4.6 mg riboflavin/kg of feed was suggested. Based on the maximum feed intake (834 g) observed for birds to reach maximum body weight (593 g) at 21 days of age, a minimum intake of approximately 6.5 micrograms riboflavin/g body weight was needed for maximum performance.