Thermography is a technique to measure the body surface temperature and is used in medical applications. We evaluated its prognostic value in 340 female patients with unilateral invasive breast cancer without distant metastases. The difference of mean temperatures of the tumor area and corresponding area of the contralateral breast was defined as AT. The patients with hot tumors (delta T > or = 0.9 degrees C) had significantly worse disease free and specific survival than those with cold tumors (delta T < 0.9 degrees C) (p = 0.0003 and p < 0.0001, respectively). AT was significantly correlated with tumor size, histological nodal status and nuclear grade, positively. But AT did not have any relation with estrogen receptor status. Multivariate analyses including those conventional prognostic factors showed that AT was a marginally significant prognostic factor for disease-free survival (hazard ratio (HR) = 1.62; 95% confidence interval (CI) = 0.99-2.66, p = 0.0557) and an independent significant prognostic one for disease specific survival (HR = 1.95; 95% CI = 1.09-3.49, p = 0.0251). However, AT did not have prognostic impact on the node negative patients. AT might be a useful prognostic factor in node positive breast cancer, especially in patients who plan to be treated with preoperative systemic therapy.