The aim of this study was to compare the efficacy of three types of treatments in the periarthritis of the shoulder: corticosteroid injections, Low Level Laser Therapy (LLLT) or wait-and-see-policy. BACKGROUND DATA: Low level laser irradiation is a treatment method widely used in medical science. Many disorders, such as osteoarthritis and musculoskeletal conditions with pain, have been treated with LLLT. METHODS: Patients, suffering from periarthritis of the shoulder of at least 6 weeks' duration, were recruited by family doctors. We randomly allocated eligible patients to 6 weeks of treatment n. 20 (33%) with corticosteroid injection, n. 21 (35%) with LLLT and with wait-and-see policy n.19 (31%). We applied a number of 12 sessions with infrared Diode Laser Ga-As (904 nm), 60 W maximum power, peak power per pulse 27 W, pulse frequency 1280 Hz, average point region 2-8 J; dose/point = 3-4 J; total energy density 24 J/cm2. Outcome measures included general improvement, severity of the main complaint, pain, shoulder disability, and patient satisfaction. Severity of shoulder complaints, abduction and elevation of the arm, and the pressure pain threshold were assessed. The principal analysis was done on an intention treatment basis. We assessed all outcomes at 3,6, 12, 26, 52 weeks. RESULTS: We randomly assigned 60 patients. At 6 weeks, corticosteroid injections were significantly better than all other therapy options for all outcome measures. Success rates were 90% (18) compared with 52% (11) for LLLT and 35% (7) for wait-and-see policy. Long-term differences between injections and LLLT were significantly in favour of LLLT. Success rate at 52 weeks were 14 (70%) for injections, 19 (90.5%) for LLLT, and 16 (84%) for wait-and-see policy. LLLT had better results than a wait-and-see policy, but differences were not significant ( p < 0.0001). CONCLUSIONS: Patients should be properly informed about the advantages and disadvantages of the treatment options for the periarthritis of the shoulder. The decision to treat with LLLT or to adopt a wait-and-see policy might depend on available resources, since the relative gain of LLLT is better, but also small at long-term.