The distribution of Xylella fastidiosa, the bacterium that causes phony peach disease, was studied in roots of 10 Flordaking peach scions grafted on Nemaguard rootstock. X. fastidiosa was detected in all trees, whether symptomatic or asymptomatic for phony peach disease. Populations of X. fastidiosa in the root xylem fluid of symptomatic trees were high, and the distribution of these bacteria was uniform both along the length of roots and among roots within the root ball. In asymptomatic trees, the distribution of infected roots among the quadrants of the root ball was variable. The distribution of X. fastidiosa was not influenced by the distance the root sample was taken from the trunk or the diameter of the root piece sampled. The minimum sample size required to detect X. fastidiosa in the roots of asymptomatic peach trees, at a risk of 5%, was five to 10 roots.