[Purpose] To investigate if joint mobilization in patients with subacromial pain syndrome has additional benefits to a home training program on shoulder function and pain, and to compare home training to no physical therapy. [Participants and Methods] Eighty-nine primary care patients (mean age 45 years) with subacromial pain syndrome during an average of 23 weeks. Home training was performed twice a day during a 12 week period. One of the intervention groups received add-on shoulder joint mobilization to the home training. A third group did not receive any physical therapy. Constant-Murley score, pain and active range of motion was evaluated at baseline, 6 weeks, 12 weeks and 6 months. [Results] The total Constant-Murley score revealed no significant differences between groups at any time point. All groups improved over time. The add-on joint mobilization group reached clinical important change at 12 weeks. The subscale pain showed that both intervention groups reported less pain after 12 weeks compared to the reference group. [Conclusion] Home training is not superior to no treatment evaluated with the total Constant-Murley score. However, home training with or without add-on joint mobilization may decrease pain compared to no treatment.