The authors measured the thickness of the medial, central, and lateral bands of the plantar fascia using ultrasonographic techniques in 109 symptomatic patients with 211 painful heels. Plantar fasciitis was diagnosed by the presence of plantar heel pain and tenderness of the plantar fascia on palpation and was correlated with plantar fascia thickness. All of the symptomatic feet had medial band tenderness, with an average thickness of 5.9 mm, 68% had central band tenderness, with an average thickness of 5.3 mm, and 26% had lateral band tenderness, with an average thickness of 4.4 mm. The average thickness of all symptomatic bands was 5.35 mm, which was significantly greater than that for all asymptomatic bands, which was 2.70 mm. There were also significant differences in the thickness of the three plantar fascia bands in symptomatic patients. A plantar fascia index was established consisting of the ratio of the mean thickness of symptomatic medial, central, and lateral plantar fascia bands to that of asymptomatic bands; for this study, the index value is 1.98 (5.35/2.70 mm).