The aim of this study was to evaluate the incidence of thromboembolic events in patients with giant left atrium ( > 6.5 cm) after mitral valve replacement. From January 2000 to September 2002, a total of 126 patients who had undergone mitral valve replacement were divided into two groups according to the presence or absence of giant left atrium. Group A comprised 34 patients with left atrium over 6.5 cm without compression symptoms and Group B comprised 92 patients. The preoperative variables did not distinguish the patients in each group, except for atrial fibrillation; Group A 85.2% and Group B 61.9% ( p < 0.01). After mitral valve replacement, left atrium mean diameter was significantly decreased in Group A from 8.1 +/- 1.3 mm to 6.2 +/- 1.6 mm ( p < 0.01). There were no significant differences in thrombosis, hemorrhage and thromboembolism rates in both groups. Postoperative clinical and hemodynamic parameters demonstrated a positive clinical response to mitral valve replacement in patients with giant left atrium. During follow-up no direct relationship between thromboembolism and giant left atrium was evident.