OBJECTIVE: To analyze chromosome damage and its possible influencing factors in patients with occupational chronic benzene poisoning. METHODS: Fifty patients with occupational chronic benzene poisoning were selected as chronic benzene poisoning group,and 53 workers without occupational exposure to benzene and other toxic substances were chosen as control group by using convenience sampling method. Questionnaire and routine blood test were conducted on all study subjects. Micronucleus rate test was performed by micronucleus blocking cytokinesis assay. RESULTS: Peripheral blood tests of chronic benzene poisoning group showed significantly reduced hemoglobin level,counts of red blood cells,white blood cells,platelets,lymphocytes and neutrophils( P < 0. 01),and higher lymphocyte micronucleus rates compared to control group( !: 6. 26‰ vs 3. 91‰,P < 0. 01). The proportion of increased lymphocyte micronucleus rate in chromic benzene poisoning group was also higher than that in control group( 46. 0% vs 5. 7%,P < 0. 01). The multivariate Poisson analysis results indicated that the time after disengagement from benzene exposure was the influencing factor of micronucleus rate in chronic benzene poisoning group( P < 0. 05),after adjusting the confounding factors of gender,age,smoking status,alcohol drinking status and working age of benzene exposure. CONCLUSION: Occupational chronic benzene poisoning leads to increase of chromosome damage in lymphocytes of patients. The time after disengagement from benzene exposure was positively correlated with chromosome damage.