BACKGROUND Serum albumin (ALB) may be low during acute inflammation, but it is also affected by nutritional status. Therefore, we hypothesized that ALB and the C-reactive protein/ALB ratio (CRP/ALB) may be associated with disease activity in patients with Crohn's disease (CD). MATERIAL AND METHODS Altogether, 100 patients with CD and 100 age- and sex-matched healthy volunteers were retrospectively enrolled in the current study. The patients with CD were subdivided into patients with active disease (Crohn's Disease Activity Index >150) and those in remission. ALB levels, CRP levels, and lipid profiles were measured. RESULTS ALB and CRP levels and the CRP/ALB ratio were the most useful for differentiating between active and nonactive CD. ALB levels (r=-0.50, P<0.01), CRP levels (r=0.39, P<0.01), and CRP/ALB ratio (r=0.42, P<0.01) all correlated with CD activity. These correlations were more prominent in males. Receiver Operating Characteristic (ROC) analysis indicated that the area under the curve (AUC) representing ALB (0.79) was higher than the AUC representing CRP (0.73) or CRP/ALB ratio (0.75; P>0.05). The AUCs corresponding to ALB level, CRP level, and CRP/ALB ratio were more prominent in males versus females (P<0.05). CRP level (14.55 mg/L), ALB level (34.35 g/L), and CRP/ALB ratio (0.69) had sensitivities of 67.7%, 72.6%, and 59.7%, and specificities of 73.7%, 78.9%, and 81.6%, respectively, for CD activity. CONCLUSIONS In the present retrospective study, we found that ALB level and CRP/ALB ratio were useful biomarkers for identifying CD activity, especially in males. These results suggest that, in addition to inflammation, assessment of patient nutritional status could also aid in identifying CD activity.