It was reported in a published article, that a thin 59-year-old woman presented to the emergency department with a 3-day history of severe pain and decreased mobility of her left shoulder after receiving PNEUMOVAX 23 vaccine injection in the left deltoid approximately 2 hours prior to the onset of symptoms. Just before presenting to the emergency department, she noted swelling and redness of the soft tissue overlying the anterior aspect of her shoulder and an elevated temperature of 99.9F. Ten years prior she had received a deltoid PNEUMOVAX 23 vaccine with no adverse reaction. Information regarding which arm was injected in the previous vaccination was not available. Her medical history was significant for asthma. On examination, she had a temperature of 97.7F, left anterior shoulder swelling, erythema, and warmth to touch, with subcutaneous swelling and erythema extending anteriorly from the shoulder to the ante-cubital fossa. She had significant pain with minimal shoulder motion in any plane. The orthopedic department was consulted for evaluation of possible septic arthritis of the glenohumeral joint. Laboratory data showed a peripheral blood white blood cell count of 10, C-reactive protein of 18.1 and erythrocyte sedimentation rate of 51. The glenohumeral joint was aspirated in the emergency department, producing a small amount of fluid that was bloody with no obvious purulence. The fluid showed a white blood cell count of 12,125 with 84% polymorphonuclear leukocytes; the Gram stain was negative. Based on the clinical presentation and laboratory data the orthopedic department admitted the patient for further evaluation of a possible septic arthritis. Multisequence magnetic resonance imaging (MRI) of the left shoulder was performed with and without contrast the MRI findings were consistent with a full-thickness tear of the anterior supraspinatus tendon with 1.2 cm proximal retraction, fluid in the subacromial/subdeltoid bursa (also reported as MRI of the affected shoulder with and without contrast showed only a partial thickness tear of the rotator cuff), and a small amount of subcutaneous edema with no evidence of abscess formation. After the results were reviewed, the patient underwent arthroscopic irrigation and debridement of her left shoulder. Antibiotics were held until intraoperative cultures were obtained. Substantial inflammation was noted throughout the shoulder with no evidence of purulent material. The articular cartilage did not appear damaged. The biceps tendon was intact and appeared normal. A small partial-thickness tear involving the anterior aspect of the rotator cuff was present, with no evidence of a full-thickness tear. Some of the friable inflammatory tissue was collected for culture. Total irrigation amounted to 4.5 L of normal saline. She was prescribed 1g of cefazolin intravenously every 8 hours. Postoperative, she improved clinically in regard to her pain level and range of motion (ROM) of the shoulder. She remained afebrile, and all cultures remained negative. After 72 hours, antibiotics were discontinued and she was discharged. She was seen at 2, 6, and 12 weeks postoperatively, with ROM improving with physical therapy at each visit. She was released from follow-up at 12 weeks, with ROM nearly equal to the contralateral shoulder. The patient had a mixed laboratory picture with normal white blood cell and elevated C-reactive protein and erythrocyte sedimentation rate. Her joint fluid cell count and Gram stain were not indicative of septic arthritis, but her clinical presentation was suspicious. Given her clinical presentation, it was felt that the potential risk of articular cartilage damage from possible septic arthritis necessitated an arthroscopic irrigation and debridement. After a discussion with the patient regarding the risks and benefit of surgery, she elected to proceed with surgery. In reporting the case of pseudoseptic arthritis following PNEUMOVAX 23, the author hypothesized that, due to its multivalent composition PNEUMOVAX 23 might be capable of inducing a more prominent inflammatory response. In this case, the authors suspected that the vaccination was inadvertently injected into the glenohumeral joint directly through the rotator cuff, given the lack of a full-thickness tear and patient's thin body habitus. This could account for severe aseptic inflammation of the joint space with onset of symptoms soon after vaccine administration, as observed in both cases. This case further illustrates the fact that caution should be taken when injecting a vaccination in the area of the upper deltoid. Additional information has been requested.