Objectives: Anaemia has been reported to be present in 1 to 11% of dental patients. However, little is known about the prevalence of anaemia in relation to specific oral diseases. This study compared the prevalence of anaemia in adults with 7 types of oral disease, adjusting for age and gender.Patients and Methods: Preoperative values for haemoglobin, haematocrit, and red blood cell count were retrospectively reviewed for 5032 consecutive adult dental inpatients (2650 males, 2382 females).Results: Logistic regression analysis showed that the prevalence of anaemia in patients with oral cancer was 7 to 9 times higher than that in patients with impacted teeth (odds ratio, 7.0; 95% confidence interval, 4.4–11.1 judged from haemoglobin; odds ratio 8.0; 95% confidence interval, 4.8–13.6 from haematocrit; odds ratio 9.2; 95% confidence interval, 6.0–13.9 from red blood cell count). Similarly, anaemia was 3 to 4 times more prevalent in patients with oral inflammation (odds ratio, 3.2; 95% confidence interval, 2.1–5.1 from haemoglobin; odds ratio, 3.7; 95% confidence interval, 2.2–6.1 from haematocrit; odds ratio, 3.7; 95% confidence interval, 2.5–5.5 from red blood cell count) or trauma (odds ratio, 2.6; 95% confidence interval, 1.6–4.1 from haemoglobin; odds ratio, 2.7; 95% confidence interval, 1.5–4.6 from haematocrit; odds ratio, 3.1; 95% confidence interval, 2.0–4.8 from red blood cell count) and 2 to 3 times more prevalent in patients with benign tumours (odds ratio, 2.5; 95% confidence interval, 1.5–4.1 from haemoglobin; odds ratio, 2.6; 95% confidence interval, 1.5–4.6 from haematocrit; odds ratio, 2.8; 95% confidence interval, 1.8–4.3 from red blood cell count) or oral cysts (odds ratio, 1.7; 95% confidence interval, 1.1–2.8 from haemoglobin; odds ratio, 1.9; 95% confidence interval, 1.1–3.2 from haematocrit; odds ratio, 2.1; 95% confidence interval, 1.4–3.2 from red blood cell count) than that in patients with impaction. Differences in prevalence of anaemia between patients with oral diseases remained significant after adjusting for gender and age.Conclusion: Patients with oral cancer, oral inflammation, oral trauma, benign oral tumours, or oral cysts had a higher prevalence of anaemia than that of patients with impacted teeth, irrespective of age or gender. Anaemia is most prevalent in patients with oral cancer and least prevalent in those with impacted teeth or jaw deformities.