Thromboembolic event (TEE) is the most common complication and a second cause of mortality in cancer patients. Multiple hypotheses for occurrence of TEE have been proposed. There are no reports on the frequency/impact of TEE in localized gastroesophageal cancer patients. We hypothesized that TEE at baseline and during chemoradiotherapy (CTRT) in gastroesophageal cancer patients would have an impact on overall survival (OS) of these patients. All consecutive patients with gastroesophageal cancer undergoing CTRT from 2001 to 2004 were eligible for this analysis. Baseline and subsequent TEEs were documented and correlated with patient characteristics and OS. One hundred ninety-eight patients were analyzed. TEEs were documented in 9.6% of the patients. At baseline, TEEs were documented in 4.0% of the patients. During CTRT, TEEs were documented in 6.1% of the patients. Pulmonary embolism (43.5%) and lower extremity venous thromboses (39%) were the most frequent TEEs. Median OS for patients with a TEE occurring at anytime was 17.7 versus 32.0 months for patients who never developed a TEE (P = 0.014). TEEs at baseline correlated with poor median survival: 13.1 versus 30.7 months for those without a TEE (P = 0.029). In a multivariable analysis, TEE at baseline and/or during CTRT was an independent predictor of OS (hazard ratio, 1.818; P = 0.040). Our data are the first to document the frequency of TEE in gastroesophageal cancer patients undergoing CTRT, and that TEE is an independent prognosticator of OS. Active research to prevent and treat TEEs is needed to improve survival of patients with localized gastroesophageal cancer.