It has long been suspected anecdotally that needle aspiration or contrast arthrogram before bone scan may cause a false-positive bone scan. This dictum often directs the sequence of events in the clinical workup of joint disease, yet data to support or refute this are lacking. This study was undertaken to generate such data. Fifty-six joints in mature dogs were examined, including hips, knees, elbows, and shoulders. The joints were examined in pairs; one joint was injected with Conray 60 for an arthrogram, and the contralateral joint was injected with an equal volume of normal saline to simulate a joint aspiration. Confirmation of needle placement and injection into the joints was made with fluoroscopic and digital subtraction imaging. Numbers of attempts required for aspiration and quantity of contrast material extravasated were noted for each joint. Baseline 99mTc-HDP or 99mTc-MDP bone scans were done before the experimental joint aspirations, with follow-up scans at 24 and 96 hr. The scans showed no significant change from baseline after either needle aspiration or arthrogram. When the diagnostic workup suggests the need for such a procedure, it should be performed. In contradiction to popular belief, joint aspiration and/or arthrogram did not affect a subsequent bone scan.