Hydroxyapatite (HA) crystal deposition disease (HADD) is a well-recognized systemic disease of unknown etiology that is caused by para-articular and/or intra-articular deposition of HA crystals. The disease is clinically manifested by localized pain, swelling, and tenderness about the affected joint along with variable limitation of joint motion, although not all patients are symptomatic. Plain radiographs may show calcifications of varying size and shape in the para-articular tendons, bursae, and capsule. The disease may be mono- or polyarticular in distribution. The shoulder is most commonly involved with calcification in the supraspinatus tendon. When intra-articular, HA crystals can cause joint destruction. Any joint can be involved; the shoulder is most commonly affected, resulting in "Milwaukee shoulder." Treatment of HADD usually requires use of analgesics, local heat, needling with or without aspiration of the calcific deposits, steroid injections, and, at times, even surgery for relief of pain.