Recently, a high percentage of adults with isolated secundum atrial septal defects (ASD) and ventricular septal defects (VSD) undergoing surgical repair had a circumferential pericardial effusion (PE), preoperatively. It was our impression that PEs are uncommon in children with unrepaired ASD or VSD. To evaluate this impression, we performed a retrospective study to determine the prevalence of PE in children with ASD compared with those with VSD and with children with normal cardiac anatomy. The preoperative echocardiograms of 90 patients with isolated surgical grade secundum ASDs, 75 patients with isolated VSDs, and 91 normal patients were reviewed to evaluate for the presence or absence of pericardial effusions and also the septal defect size. Only 1 patient (ASD group) of the total 256 had a global PE (0.4%). No large effusions were found in any group. Eighty-one children (32%) had any effusion present in the pericardial space. The prevalence of these small PEs was not significantly different between the ASD (36/90, 40%) and VSD (23/75, 31%, p = 0.25) groups. The patients with ASD, however, had a significantly higher prevalence of PEs compared with the control group (22/91, 24%, p <0.03). In conclusion, the presence of global PEs in children with surgical grade ASD or patients with VSD is rare, unlike that reported in adults with the same lesions. Trace effusions are found more commonly in children with ASD than those in VSD or in normal children, which may herald a potential for larger effusions with a longer time before defect closure.