The objective of the study is to compare the efficacy of electro-acupuncture with placebo-acupuncture for the treatment of shoulder pain. This study comprised of a prospective, randomized, placebo controlled trial, with independent evaluator set in a Public primary care clinic in Spain. The participants are patients aged from 25 to 83 years with shoulder pain. Patients were randomly allocated to two treatments over eight weeks, with electro-acupuncture or skin non-penetrating placebo-acupuncture, both able to take diclofenac if needed for intense pain. Primary outcome measure was the difference between groups in pain intensity (visual analogue scale-VAS). Secondary outcomes were differences between groups in pain intensity measured by Lattinen index, in range of motion (goniometer), functional ability (SPADI), quality of life (COOP-WONCA charts), NSAIDS intake, credibility (Borkoveck and Nau scale) and global satisfaction (10 points analogue scale). Assessments were performed before, during and three and six months after treatment. At six month follow-up after treatment the acupuncture group showed a significantly greater improvement in pain intensity compared with the control group [VAS mean difference 2.0 (95% CI 1.2-2.9)]. The acupuncture group had consistently better results in every secondary outcome measure than the control group. Acupuncture is an effective long-term treatment for patients with shoulder pain (from soft tissues lesions) in a primary care setting.