Collagen, a major component of the extracellular matrix, is significantly upregulated in colorectal liver metastasis (CRLM) compared to liver tissue. Expression levels of specific collagen types in CRLM resemble those in colorectal cancer (CRC) and colon tissue. We investigated whether the collagen hydroxylation pattern from the primary tumor also migrates with the metastatic tumor. The degree of collagen alpha-1(I) hydroxylation in colon, CRC, liver, and CRLM tissue in the same individuals (n=14) was studied with mass spectrometry. The degree of hydroxylation was investigated in 36 collagen alpha-1(I) peptides, which covered 54% of the triple helical region. The average degree of hydroxylation in liver tissue was similar to that in colon tissue. The overall degree of hydroxylation was significantly lower (9% +/- 14%) in CRC tissue and also significantly lower (12% +/-22%) in CRLM tissue compared to colon or liver tissue. Still, in previous research of liver and CRLM enzymes involved in collagen hydroxylation were found to be upregulated, whereas P4HB (4-prolyl hydroxylase beta unit) was downregulated. Furthermore, 11 peptides are present with a specific number of hydroxylations that are significantly different between CRLM and liver tissue; these peptides could be candidates for the detection of CRLM. For one of these eleven peptides, a matching naturally occurring peptide in urine has been identified as being significantly different between patients suffering from CRLM and healthy controls. We conclude that the degree of hydroxylation in CRC and CRLM tumor tissue is in general significantly downregulated in comparison to healthy colon and liver tissue. The hydroxylation pattern in CRLM resemble partly the pattern in liver, primary colorectal cancer and colon.