Adhesive capsulitis (AC) is a common pathological condition of the shoulder characterized by painful restriction of range of motion (ROM) of the glenohumeral joint. Currently, no consensus has been reached regarding the best treatment. Hyaluronic acid (HA) injection is a safe procedure that can result in significant improvement in active and passive ROM, alleviating pain and improving shoulder function. We systematically reviewed current literature in order to evaluate the best evidence about the effectiveness of intra-articular HA injection for the treatment of primary AC. We searched Medline, CINAHL, Embase, Google Scholar and Cochrane Library. We selected studies comparing clinical outcomes of patients treated with HA in association or not with conventional therapy. Seven studies were evaluated: 2 uncontrolled randomized studies and 5 prospective randomized clinical trials with level of evidence I. Clinical outcome measures used included, among other, ROM, Visual Analogic Scale (VAS) pain scores, Constant score, Activity of daily living, Shoulder Pain and Disability Index (SPADI), American Shoulder and Elbow Surgeons (ASES) and Japanese Orthopedic Association Score (JOA score). Improvement was noted in terms of ROM, constant scores and pain in patients affected by AC treated with intra-articular HA injections. When compared with cortisone intra-articular injection, HA has equivalent clinical outcomes and ROM. The heterogeneity of treatments used in the studies reviewed, makes it difficult to draw a definite conclusion on the subject. HA injections do not seem to determine the final outcomes directly compared with conventional treatments. However, they could play an important role for early mobilization in the initial stages, during which, due to pain and inflammation, the patient keeps the shoulder immobilized for a long time, determining the direct cause of AC. Numerous variables, including use of lidocaine, different HA and AC stages, could influence the results and deserve to be accounted for in future investigations.