We present a prospective study on the long-term efficacy of percutaneous ethanol injection (PEI) treatment of a large series of symptomatic thyroid cystic nodules (STCN). Ninety-eight patients (72 females and 26 males) were treated. The mean basal volume of the STCN was 35.3 mL. In 92 of 98 patients PEI treatment induced a greater than 50% nodule shrinkage, only 6 of 92 responder patients relapsed at a follow-up of 9 years. Moreover, all the patients had a significant clinical benefit because a significant reduction of the cyst-associated symptoms was recorded. Furthermore, a limited number of sessions was required for the treatment of cysts larger than 40 mL (mean +/- standard deviation [SD]: 2.7 +/- 0.75) demonstrating the feasibility of the procedure also in the treatment of large cysts. In conclusion, PEI is an effective and inexpensive procedure with a high patient compliance and long-lasting effects in the treatment of cysts larger than 40 mL.