PURPOSE: To examine factors associated with smoking cessation at pregnancy onset in Hispanic women. DESIGN: Cross-sectional analysis of baseline data from the prospective Latina Gestational Diabetes Mellitus Study. SETTING: Public obstetrical practices of a medical center in Massachusetts, 2000-2004. SUBJECTS: A total of 351 Hispanic (predominantly Puerto Rican) prenatal care patients who smoked in the year prior to pregnancy. MEASURES: At enrollment, interviewers collected self-reported cigarette smoking prior to and during pregnancy and sociodemographic, health, and acculturation factors. ANALYSIS: Logistic regression and backward elimination procedures were used to determine factors independently associated with quitting. RESULTS: Forty-five percent of women reported quitting smoking at pregnancy onset. In multivariate analyses, women born outside the United States, women with a family history of diabetes, and non-Puerto Rican Hispanics were 32% to 54% more likely to quit smoking. Women with high stress, women with marijuana use, and parous women were 23% to 49% less likely to quit. Women who smoked 20+ cigarettes/d in prepregnancy were less likely to quit smoking (relative risk  =  .44; 95% confidence interval .27, .65) compared with light smokers. Age, income, body mass index, language preference, prepregnancy exercise, and alcohol consumption were not associated with quitting. CONCLUSIONS: Non-U.S. birthplace, family history of diabetes, and non-Puerto Rican ethnicity were associated with quitting smoking at pregnancy onset in Hispanic women. Prepregnancy marijuana use and smoking, parity, and stress were associated with continued smoking.