In this study, we aimed to determine the frequency of pericardial effusion (PE) in children diagnosed with acute lymphoblastic leukemia (ALL). Clinical features of patients with effusion were evaluated. For this purpose, we reviewed the medical records of ALL patients who had pretherapy echocardiograms. A total of 90 patients aged between 1.8 and 16.3 years were analyzed retrospectively. In 23 of 90 (25.6%) patients, PE was detected at initial diagnosis. The age of patients with PE ranged between 1.8 and 14.8 years (mean 5.05 +/- 3.77 years). The female/male ratio was 9/14. Six (26.1%) patients were T-lineage and 17 (73.9%) were B-lineage ALL. Nine (39%) patients were in standard risk group, 13 (57%) were in median risk group, 1 (4%) patient was in high-risk group. Mean initial white blood cell count was 40.756 +/- 38.653/mm(3) (range 23.000-130.000/mm(3)). Mean initial hemoglobin count was 7.3 +/- 1.39 gr/dL (range 5.5-10.1 gr/dL), mean initial platelet count was 35.200 +/- 26.300/mm(3) (range 4.000-118.000mm(3)). Size of effusions was between 2 and 6 mm (mean size 3.3 +/- 1.8 mm). All patients had normal left ventricular systolic function. In 87% of patients, effusions disappeared in the first 7 days and, in 13%, disappeared between 8th and 15th days of chemotherapy. None of the patients required pericardiocentesis. Cardiac dysfunction did not occur among any of these patients during chemotherapy.