We studied five fresh-frozen lower extremity cadaveric specimens to assess the effect of knee effusions on KT-1000 arthrometry. Part 1 consisted of serial 10-ml injections (up to 100 ml) of saline into each knee and measurements of midpatellar knee circumference and anterior displacement using the KT-1000 arthrometer at 67, 89, and 134 N after each 10-ml increment. Part 2 consisted of evacuation of the saline and transection of the anterior cruciate ligament through a 2-cm medial parapatellar arthrotomy. Each knee again underwent the part 1 protocol. Sequential injections in parts 1 and 2 showed incremental increases in knee circumference and KT-1000 arthrometer measurements for all three force levels. A 3-mm increase in anterior translation compared with the value at 0-ml injection was obtained by the 70-ml injection point in both groups. At the 70-ml injection point, the patella was ballottable, thereby affecting anterior measurements - despite posterior force on the patella sensor pad - because of the KT-1000 arthrometer reference level at midpatella. This increase in KT-1000 arthrometer readings could erroneously imply anterior cruciate ligament disruption in the clinical situation of right-to-left comparison. We conclude that clinicians using the KT-1000 arthrometer should aspirate knees that have effusions and a ballottable patella to minimize false-positive readings.