Data on the relationship between aging, chemotherapy, and risk for venous thromboembolism (VTE) are controversial. We sought to evaluate the risk of chemotherapy-associated VTE in young to middle-aged (YMA) and elderly cancer patients and to analyze the VTE-free survival time in both groups. Patients with histologically confirmed diagnosis of solid malignancy receiving any type of systemic chemotherapy, no clinical diagnosis of VTE before chemotherapy initiation, and Eastern Cooperative Oncology Group (ECOG) performance status (PS) ≤2 were enrolled in this study. Of the 486 consecutive patients included in the study, 380 (78%) were classified as YMA (≤70 years of age) and 106 (22%) as elderly (>70 years of age). At a median follow-up of 1 year, the incidence of VTE events was almost two-fold greater in elderly than in YMA (11% vs. 6%). Age (≤70 years vs. >70 years (hazard ratio [HR], 2.42; 95% confidence interval [CI] 1.15-5.06; p=0.020), ECOG-PS (HR, 6.54; 95% CI 3.10-13.8; p<0.0001), and platinum-based chemotherapy (HR, 2.46; 95% CI 1.06-5.69; p=0.035) were independent risk factors for VTE. In the elderly subset, a trend toward an increased risk of VTE in patients receiving a platinum-based chemotherapy when compared with a non-platinum-containing regimen was observed (15% vs. 9.1%). The Kaplan-Meier analysis showed that elderly patients had a significantly shorter VTE-free survival time compared with younger cancer patients (log-rank test=2.0; p=0.045). Our study reports an increase incidence of VTE in elderly cancer patients treated with chemotherapy compared with the younger group, suggesting that aging is one of the most important risk factors for VTE. On the basis of the results of this study, we believe that a validated predictive model including age, ECOG-PS, and type of chemotherapy (platinum- vs. non-platinum containing regimen) would enable clinicians to target thromboprophylaxis to those patients considered to be at greatest risk.