BACKGROUND: Inflammatory bowel disease manifests throughout all ethnic groups. Antisaccharomyces cerevisiae (ASCA) and antineutrophil cytoplasmic antibodies (pANCA) can aid in the differentiation between Crohn's disease (CD) and ulcerative colitis (UC), but their sensitivity may vary between races. OBJECTIVES. This study compared the sensitivity, specificity, and positive and negative predictive values (PPV, NPV) of pANCA and ASCA between Chinese and Caucasian IBD populations and identified disease subtype associations. RESULTS: Three hundred patients were prospectively recruited from Caucasian and Chinese populations (CD, n = 50, UC, n = 50, controls, n = 50 each). pANCA detection was greater in Caucasian than Chinese UC patients (p = 0.046). ASCA IgG detection was similar, but IgA was lower in Chinese CD patients (p < 0.001). Differentiation between UC and CD (+ve pANCA/-ve ASCA) demonstrated a PPV of 92% in isolated colonic disease. Logistic regression in CD identified positive pANCA had a lower association with ileal (OR = 6.8, p = 0.0067) and complicated disease (OR = 5.5, p = 0.015). Caucasian CD patients with positive ASCA IgA/IgG had a greater association with ileal (OR = 6.7, p = 0.022) or complicated disease (OR = 9.4, p = 0.0073) and in Chinese CD patients positive ASCA IgA/IgG was associated with isolated ileal disease (OR = 16.8, p = 0.032). Linear regression demonstrated that higher ASCA titers predicted complicated CD and isolated ileal disease. CONCLUSIONS: This study identified that pANCA is more sensitive in Caucasian than Chinese UC and that ASCA IgA has a low yield in Chinese CD. pANCA and ASCA are useful for differentiating between UC and CD in both populations, and ASCA IgG and IgA titers have potential use in determining the risk of developing complicated CD.