[en] Background: Crohn's disease (CD) is a polygenic multifactorial heterogeneous disease. Anti-Saccharomyces Cerevisiae antibodies (ASCA) correlate highly with CD and are present in 50-80% of patients. The reason for ASCA positivity or negativity in CD is unknown. The aim of our work was to analyse clinical, epidemiological and genetic characteristics in ASCA + or ASCA- CD patients. Methods : 113 patients with CD were tested for ASCA (IgA and IgG) by using a commercial kit (Medipan Diagnostica). Age, gender, systemic manifestations, familial form of disease, age at diagnosis, location and behaviour of the disease, smoking habit as well as genotyping for -308 TNF gene polymorphisms were determined. Results : 38.9% CD patients were negative for both IgA and IgG ASCA while 61.1% were ASCA positive (respectively IgA and IgG : 31.9%; IgA only : 9.7%; IgG only : 19.5%). The only significant difference between ASCA+ and ASCA- patients was for smoking habit : there were 29% smokers in ASCA+ versus 50% in ASCA- CD patients (P = 0.03). This low proportion of smokers was more prominent in ASCA IgA+ patients than in isolated ASCA IgG+ patients (25.6% versus 45.5%) and was minimal in patients with high titers of ASCA IgA (0/8). Logistic regression showed smoking habit still borderline for significance (P = 0.057). Conclusions : Our results suggest a negative association between smoking and ASCA positivity in CD. This association was more prominent for ASCA IgA+. It indicates that smoking habit should be taken into account when analysing ASCA status in CD patients and may suggest an influence of smoking on immunization against intestinal material.