Pericardial effusion, a sign of cardiac perforation, may complicate permanent pacemaker placement. Risk factors for development of post-permanent pacemaker effusion have not been evaluated. The purpose of this study was to determine the predictors of symptomatic pericardial effusion after permanent pacemaker placement. The Mayo Clinic pacemaker and echocardiogram databases were cross-referenced. From 1995 to 2003, 4,280 permanent pacemakers were implanted. Fifty (1.2%) patients developed significant effusion and symptoms consistent with perforation. They were randomly matched with 100 patients without effusion after permanent pacemaker placement. The strongest predictors of postimplant effusion by univariate analysis were the concomitant use of a temporary transvenous pacemaker (hazard ratio [HR] 3.2, 95% confidence interval [CI] 1.6-6.2, P = .001) or steroid use within 7 days prior to implant (HR 4.1, 95% CI 1.1-10, P = .003). Weaker predictors were use of helical screw ventricular leads, body mass index (BMI) 35 mmHg (HR 0.70, 95% CI 0.44-0.97, P = .01) or BMI >30 (HR 0.62, 95% CI 0.41-0.93, P = .01). Multivariate predictors were use of temporary pacemaker (HR 2.7, 95% CI 1.4-3.9, P = .01), helical screw leads (HR 2.5; 95% CI 1.4-3.8, P = .04), and steroids (HR 3.2, 95% CI 1.1-5.4, P = .04). Right ventricular systolic pressure >35 mmHg was the only protective factor (HR 0.70, 95% CI 0.50-0.92, P = .02). The incidence of postimplant effusions is low. In order to minimize periprocedural permanent pacemaker effusions, temporary pacemaker placement should be avoided unless essential, and particular care should be taken when placing a permanent pacemaker in patients who are taking steroids.