Mannose-binding lectin (MBL) deficiency is associated with increased susceptibility to airways infections and autoimmunity. We examined whether MBL deficiency was more common in COPD patients, and whether MBL deficiency was associated with COPD severity. 415 COPD patients and 231 healthy subjects, aged 40-75, were examined in 2006/07. Plasma MBL levels were determined by ELISA. Low or deficient MBL levels were defined as plasma levels below 500ng/mL or 100ng/mL respectively. Logistic regression models determined factors associated with MBL deficiency; with explanatory variables study category, sex, age, smoking, comorbid heart disease, and CRP. For COPD severity, explanatory variables were FEV1, exacerbation history, hypoxia, respiratory symptoms, inhaled steroids, and CRP. 18.2% of healthy subjects and 22.2% of patients had MBL levels below 100ng/mL (p=0.23); 42.9% of healthy subjects and 49.6% of patients had levels below 500ng/mL (p=0.10). After adjustment for co-variables, patients had an OR (95% CI) of 1.26 (0.7, 2.2) for having MBL levels below 100ng/mL compared with healthy subjects, and an OR (95% CI) of 1.06 (0.7, 1.7) for having levels below 500ng/mL. Among the COPD patients, none of the disease variables were associated with MBL deficiency. No association was found between MBL deficiency and COPD or COPD severity.