Background: We report a rare case of calcific tendinopathy in the posterior tibial tendon (PTT) at the navicular insertion. Case: Conservative treatments other than extracorporeal shock wave therapy (ESWT) were ineffective. Calcium deposition disappeared from the PTT on plain radiographs at 6 months after ESWT. Discussion: In this case, a 14-year-old boy with calcific tendinopathy of the PTT who had not benefited from conservative treatments was effectively treated using ESWT.