Plantar fascia rupture is an occasional complication in patients with chronic plantar fasciitis or in patients with plantar fasciitis treated with steroid injection. Very few cases of spontaneous plantar fascia rupture have been reported in the literature (Herrick and Herrick, Am J Sports Med 1983;11:95; Lun et al, Clin J Sports Med 1999;9:48-9; Rolf et al, J Foot Ankle Surg 1997;36:112-4; Saxena and Fullem, Am J Sports Med 2004;32:662-5). Spontaneous medial plantar fascia rupture in a 37-yr-old man with no preceding symptoms or steroid injections was confirmed with diagnostic ultrasound, which revealed severe fasciitis at the calcaneal insertion with partial tearing. After conservative treatment, the patient returned to full activities. We discuss the anatomy, risk factors, examination findings, and treatment for this condition, as well as the unique benefits that ultrasound offers over magnetic resonance imaging. It is important to consider plantar fascia rupture in patients with hindfoot pain and medioplantar ecchymosis, particularly if an injury occurred during acceleration maneuvers. Ultrasound in these cases can be used to diagnose a plantar fascia tear quickly, accurately, and cost-effectively.