Pericardial effusion is an infrequent but life-threatening complication that occurs after hematopoietic stem cell transplant (HSCT). The present study aimed to analyze the etiology and outcome of patients who developed the entity. A retrospective analysis of patients who underwent allogeneic HSCT and developed symptomatic pericardial effusion between 2017 and 2023 was performed. Of 749 patients who underwent HSCT, 22 (3%) developed symptomatic pericardial effusion. The median age was 85 months (range: 26–252). The commonest indication for HSCT was transfusion-dependent thalassemia, which was more common than in patients who did not develop pericardial effusion (82% vs. 56%, P = 0.016). All the patients who developed effusion received myeloablative conditioning. The mean duration from transplant to effusion diagnosis was 98 days (range: 22–195). Sinusoidal obstruction syndrome was observed in a higher proportion of patients who developed pericardial effusion, compared to those who did not (41% vs. 17%, P = 0.002). Fast breathing with/without dyspnea was the commonest clinical presentation, observed in 16 (73%) patients. There was evidence of cardiac tamponade in 9 (41%) patients. Calcineurin-inhibitor was withheld in 12 (54%) patients followed by a short course of glucocorticoid therapy. Sixteen (73%) patients had a complete resolution of the effusion after a mean duration of 12 days. Five patients succumbed to unrelated causes. Pericardial effusion is an infrequent but severe complication post-HSCT and tachypnea is the commonest presentation. Early identification of the etiology and appropriate management can lead to a complete resolution in most cases.