BACKGROUND: The aim was to evaluate the association between plasma tissue inhibitor of metalloproteinase-1 (TIMP-1) and serum carcinoembryonic antigen (CEA) levels and outcome in patients with metastatic colorectal cancer (mCRC) receiving XELOX (combination chemotherapy with capecitabine and oxaliplatin) as first-line treatment. PATIENTS AND METHODS: One hundred and twenty patients were included. Blood samples were collected before treatment and 3 weeks later before the next treatment cycle. Plasma TIMP-1 and serum CEA levels were correlated to treatment outcome. RESULTS: No significant associations between baseline TIMP-1 or CEA levels and best response to treatment or progression-free survival (PFS) could be demonstrated. In contrast, high baseline plasma TIMP-1 levels were associated with poor overall survival (OS), P = 0.008, hazard ratio (HR) = 1.80 [95% confidence interval (CI): 1.17-2.78]. Furthermore, increase in TIMP-1 levels from baseline to immediately before the second cycle of chemotherapy had a significant negative effect on survival (P = 0.03, HR = 1.30, 95% CI: 1.02-1.65) while a decrease in TIMP-1 was significantly associated with a higher objective response rate (P = 0.03). Conclusions: Both high baseline and subsequent increase in TIMP-1 levels were associated with shorter OS in patients with mCRC receiving XELOX as first-line treatment, whereas baseline TIMP-1 levels were not associated with response or PFS following XELOX treatment.