An In-111 WBC study showed intense periarticular uptake in both knees of a patient being investigated to exclude joint infection before total knee replacement surgery for advanced osteoarthritis. Infection was subsequently excluded. Patients with synovitis secondary to active osteoarthritis can have intense synovial uptake of labeled WBCs. This should be considered as a cause of false-positive scans in the investigation of septic arthritis with labeled WBCs.