Atrial arrhythmias (AAs) after noncardiac thoracic surgery may be associated with increased mortality, length of stay (LOS), and health care expenditures. A retrospective analysis of adult patients who underwent thoracotomy at our institution from January 2002 to June 2008 was performed. Of 820 patients identified, 112 (14%) developed an AA. Overall mortality was 7.14% in the AA group and 3.11% in the non-AA group (relative risk, 2.30; 95% confidence interval, 1.06-4.91; P = 0.035). Median intensive care unit (ICU) LOS and total LOS were 4.0 and 7.0 days in the AA group and 3.0 and 5.0 days in the non-AA group (ICU LOS P < 0.01 and total LOS P < 0.001). Median health care expenditures in the AA group were approximately $37,000 versus $28,000 in the non-AA group (P < 0.001). The development of an AA in this patient population may be associated with increased mortality, ICU and total LOS, and health care expenditures.