BACKGROUND: Children with cystic fibrosis may have a deficiency of micronutrients, including zinc, which may affect their susceptibility to infections. There is a paucity of data on zinc supplementation among children with cystic fibrosis. We hypothesized that a pharmacologic dose of zinc administered daily for 12 months would reduce the need for antibiotics by 50%. METHODS: This double-blind randomized placebo-controlled trial was conducted among children with cystic fibrosis to assess the effect of zinc supplementation on the need for antibiotics and pulmonary function tests. The children, age 5-15 y, of either sex, received either 30-mg zinc tablets or similar looking placebo tablets daily in addition to standard care. They were followed up every month for a period of 12 months and whenever they had pulmonary exacerbations. Their serum zinc was estimated at baseline and at 12 months of enrollment. During each visit, the children underwent a pulmonary function test and sputum culture. RESULTS: Of a total of 43 children screened, 40 were enrolled, and of them, 37 completed the study. The median (interquartile range) number of days of the administration of antibiotics over 12 months of follow-up among the children receiving zinc was 42 (14-97) d. In the placebo group, it was 38 (15-70) d (P = .79). There were no significant differences in the percent-of-predicted FEV1 or change in FEV1 values at 12 months (P = .44). The number of children in whose respiratory specimens Pseudomonas was isolated was similar for the 2 groups at different time intervals. The adverse events reported were similar in the 2 groups. CONCLUSION: We did not find any significant difference in the need for antibiotics, pulmonary function tests, hospitalization, colonization with Pseudomonas, or the need for antibiotics for children with cystic fibrosis receiving zinc supplementation of 30 mg/d.