We sought to evaluate the effectiveness of salt and fludrocortisone versus placebo in the prevention of syncope recurrence in children. Intravascular volume expansion with fludrocortisone and salt has been reported to be effective in the treatment of syncope in children. However, no pediatric placebo-controlled data are available on the effectiveness of this mode of therapy. Thirty-three children with syncope or severe presyncope were randomized in a double-blinded fashion to receive either fludrocortisone 0.1 mg/day and salt 1 g/day or placebo two capsules per day for one year. All children had a positive tilt test before enrollment. Thirty-two children (20 female) had follow-up. Their age was (mean +/- SD) 13.9 +/- 2.5 years. The number of syncopal episodes before therapy was 4.4 +/- 4.8. Therapy was continued for 176 +/- 117 days, and follow-up including time after discontinuation of medications was 1.2 +/- 0.8 years. The demographics were similar in the 18 children treated with fludrocortisone and salt compared with the 14 children on placebo. Data for up to one year of randomization were included in analyses. Symptoms recurred in 10 of 18 children on fludrocortisone and salt and in 5 of 14 children on placebo (p < 0.04). Children on placebo had no symptoms until they discontinued their study medications. These data, coupled with the reported comparable effect of many medications used in the treatment of syncope, raise the potential of a significant placebo effect with pharmacologic therapy.