There is currently no objective reliable diagnostic test for plantar fasciitis inasmuch as diagnosis cannot be made on the basis of finding a heel spur on radiography (x-ray). In this single-blind observational study, ultrasonography was used to measure plantar fascia thickness in subjects with clinically suspected plantar fasciitis and in control subjects. It was concluded that the population mean plantar fascia thickness is greater for people with plantar fasciitis than for people without heel pain (P < .0005) and that the difference is clinically significant. The ultrasonic appearance of the plantar fascia in plantar fasciitis indicated inflammatory changes.