Background Timely diagnosis and management of iron deficiency anemia (IDA) in colorectal cancer (CRC) patients improves overall quality of life and survival. This study assessed the proportion of CRC patients who were formally diagnosed with IDA and factors that predict a formal diagnosis of IDA and receiving iron therapy. Methods We retrieved electronic medical records (EMRs) of CRC patients from a large comprehensive cancer center in the Northeastern part of the United States (n = 499). We abstracted sociodemographic characteristics, relevant laboratory results, IDA diagnosis, and iron supplementation from the EMRs. We assessed relationships between participant characteristics, a diagnosis of IDA and receiving iron therapy through adjusted logistic regressions. Results IDA was formally diagnosed in 26 (5.2%) individuals judged by EMR documentation. Only 153 (30.7%) participants had iron laboratory results available. Among the 153 patients with iron panel data available, 113 (73.9%) had iron deficiency. Seventy-six had absolute iron deficiency as shown by ferritin levels below 100 ng/mL and iron saturation less than 20% and 37 had functional iron deficiency as shown by ferritin levels between 100 and 500 ng/mL and iron saturation less than 20%. 12% of all patients had documentation of iron therapy receipt. A formal diagnosis of IDA was not associated with any of the covariates. Conclusions Iron deficiency anemia is under-diagnosed among CRC patients and most likely under-documented in clinical notes. Rates of iron repletion are low, suggesting that many patients with IDA are untreated. Future research should explore provider-level and other strategies for improving assessment and diagnosis of IDA among CRC patients.