Background: There is an increasing trend for optical guidance techniques in surgery. Optical imaging using Diffuse Reflectance Spectroscopy (DRS) can distinguish different tissue types through a specific “optical fingerprint”. We investigated whether DRS could discriminate metastatic tumor tissue from normal liver tissue and thus if this technique would have potential for further implementation into surgical instruments or radiological intervention tools. Methods: A miniaturized optical needle was developed able to collect DRS spectra between 500 and 1600 nm. Liver specimen of 24 patients operated for colorectal liver metastases were analyzed with DRS immediately after resection. Multiple measurements were performed and DRS results were compared to the histology analysis of the measurement locations. In addition, normal liver tissue was scored for the presence or absence of steatosis. Results: A total of 780 out of the 828 optical measurements were correctly classified into either normal or tumor tissue. The resulting sensitivity and specificity were both 94%. The results of the analysis for each patient individually showed an accuracy of 100%. The Spearman's rank correlation of DRS-estimated percentages of hepatic steatosis in liver tissue compared to that of the pathologist was 0.86. Conclusions: DRS demonstrates a high accuracy in discriminating normal liver tissue from colorectal liver metastases. DRS can also predict the degree of hepatic steatosis with high accuracy. The technique, here demonstrated in a needle like probe, may as such be incorporated into surgical tools for optical guided surgery or percutaneous needles for radiological interventions.