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.