© 2015 Journal of Shoulder and Elbow Surgery Board of Trustees.Background: We evaluated the factors that affect the natural course of subacromial impingement syndrome in patients without rotator cuff tears. Methods: In total, 63 patients were included. During the first evaluation, we recorded each patient's age, gender, profession, body mass index (BMI), hand dominance, alcohol and tobacco consumption, comorbidities, causative event of pain, presence of a functional limitation, duration of symptoms, shoulder scores (American Shoulder and Elbow Surgeons [ASES], Constant-Murley, and visual analog scale), history of subacromial steroid injections, and magnetic resonance imaging (MRI) classification. A subacromial lidocaine injection test was performed to confirm the diagnosis, and patients were initially treated conservatively. Of the 63 patients, 7 underwent a subsequent surgical procedure. We recalled the patients and questioned them about recurrences. According to their answers, the patients were grouped as follows: group 1, no recurrence; group 2, relapsing course; and group 3, chronic course. We compared the groups regarding the factors proposed to affect the course of the disease. Results: The mean follow-up time was 8.45 ± 0.9 years. There were no significant differences regarding gender, profession, hand dominance, alcohol consumption, smoking, comorbidities, causative event of pain, visual analog scale score, or history of subacromial steroid injections between groups. The patients in group 1 were significantly younger than those in group 2 (P = 038). The mean BMI value of the group 1 patients was significantly lower than that of the group 3 patients (P = 034). Patients with a functional limitation besides pain tended to have a relapsing course. The Constant-Murley and ASES scores were significantly higher for patients in group 1 than for patients in group 2 (P = .024 and P = 041, respectively). The duration of symptoms was significantly shorter (<3 months) in group 1 (P = .001). Most of the patients in group 1 had reversible changes on MRI (P = 038). Conclusion: In our study, younger age, lower BMI, more functional capacity, a shorter symptomatic period, reversible changes on MRI, and higher Constant and ASES scores at the first evaluation were good prognostic factors.