Aim: The aim of this work was to estimate the prevalence of iron deficiency in patients diagnosed with colorectal cancer (CRC) and to clarify its association with patient- and tumour-related characteristics. Method: This was a single-centre registry-based cohort study. Iron status was routinely evaluated upon diagnosis of CRC, and these data were coupled with patient- and tumour-specific data from the Danish CRC Group Registry (2013–2018). Data were analysed using multivariate logistic regression. Results: Out of 846 patients, 543 (64%) were iron deficient. There was an association between increasing depth of invasion and iron deficiency, with odds ratios (ORs) of iron deficiency being 2.8 (p = 0.001, CI 1.5–5.1), 4.22 (p < 0.001, CI 2.48–7.18) and 4.63 (p < 0.001, CI 2.30–9.34) for T-stages 2, 3 and 4, respectively. Right-sided tumours had an OR of 3.54 (p < 0.001, CI 2.22–5.67) of iron deficiency compared with left-sided tumours. Tumours diagnosed through the national CRC screening programme were less likely to be associated with iron deficiency (OR 0.34, CI 0.22–0.52), while female gender was associated with an increase in the odds for iron deficiency (OR 1.91, CI 1.33–2.76). Iron deficiency was prevalent in 88% of anaemic patients and 43% of nonanaemic patients. Conclusion: Iron deficiency was highly prevalent in patients diagnosed with CRC. Increased depth of tumour invasion, right-sided location and female gender were all associated with higher odds for iron deficiency, while patients diagnosed through the national screening programme were associated with lower odds for iron deficiency. A large proportion of patients with a normal haemoglobin were also iron deficient.