Primary idiopathic adhesive capsulitis is the subset of painful stiff shoulders in which no definitive cause for the “frozen shoulder” can be identified. The incidence of adhesive capsulitis is 2% to 5% in shoulder clinics and 10% to 20% in diabetics. Adhesive capsulitis has a left-sided predominance with an age distribution between 30 and 70 years and is more common in female individuals. The duration of symptoms ranges from 12 to 42 months. When untreated, 40% to 60% of patients with adhesive capsulitis have an objective residual loss of range of motion. Why the condition resolves and why it does not occur in younger and older patients are undetermined. Arthroscopic synovial biopsies in early cases of adhesive capsulitis show increase in synovial vascularity associated with small nerves, followed by subsynovial fibroblast proliferation and capsular fibrosis in patients with longer-standing symptoms. Fibrosis of the shoulder capsule with resultant loss of capsular volume and contracture of the ligaments is the major cause for restriction of shoulder range of movement. The sub cellular events and the cytokines and the sequence of triggered genes and proteins that lead to hyperemia, neoinnervation, fibroblast proliferation, fibrosis, and bone loss in adhesive capsulitis are yet to be elucidated.