Primary dysmenorrhea (PD) is a painful menstruation that can persist for the duration of a woman’s fertile life. Non-steroidal anti-inflammatory drugs, hormonal therapy, physiotherapy techniques, etc., are the main treatments. The main objective of this study is to evaluate the effectiveness of transcutaneous posterior tibial nerve stimulation (TTNS) in PD patients. The study will consist of a single-blind randomized clinical trial, parallel-assigned with two arms. Women with PD (18–43 years) with regular menstrual cycles and at least 4 points in VAS will be randomly divided into experimental (TTNS) and placebo (simulated stimulation) groups during 12 treatment sessions (1 session/week) and several follow-ups: monthly during treatment and 1, 3 and 6 months after. Maximum and mean pain intensity, pain duration, pain severity, number of anti-inflammatory drugs, quality of life, sleep quality, overall improvement, treatment satisfaction and secondary effects will be measured once a month every 6 months and at 3 and 6 months. The Student’st-test for independent samples or the Mann–Whitney U test will be used. The literature shows effective physiotherapeutic techniques for PD in the short term, which do not act on causes and have limitations. The TTNS technique can be used in transcutaneous and percutaneous modalities, with similar effectiveness, but the transcutaneous causes less discomfort. TTNS modulates pain, and long-term benefits could be achieved at low cost and without patient discomfort.