Increasing evidence suggests that microRNAs play a key role in the initiation and progression of cancer, and therefore, may comprise a novel class of molecular biomarkers with prognostic and predictive potential. Drug resistance is a major impediment to the successful chemotherapeutic treatment of cancer. Current tests assay the ex vivo growth of a tumor in the presence of chemotherapeutic drugs but new molecular tests are needed. We extracted total RNA from 130 colorectal cancer specimens that had been previously tested in the Extreme Drug Resistance assay, a clinically validated drug resistance test. Each sample's microRNA expression pattern was assayed on an LNA (Locked Nucleic Acid) enhanced microarray platform, which allows for very sensitive and specific detection of small RNA targets like microRNAs. This study, for the first time demonstrates that the microRNA expression pattern of a tumor biopsy reflects the drug resistance status of the cancer. Our analysis enabled identification of tumors that were resistant to 5-FU/Leucovorin, Oxaliplatin, or Irinotecan, based solely on the tumor cell's microRNA profiles. Thus, we propose that a molecular Drug Resistance (mDR) assay, based on a tumor's microRNA profile can potentially provide a basis for prediction of drug response. Two advantages of such an mDR assay are that it requires very little amount of input RNA (down to 100 ng), and that it has a fast (one day) response time.