Objective To examine the effects of a Parish Nurse Intervention Program (PNIP) on maternal health behaviors, glycemic control, and neonatal outcomes among Mexican American women with gestational diabetes. Design A randomized controlled trial comparing care as usual (CAU) with a supplementary 1-hour education session for diabetes education reinforcement by a Parish Nurse. Setting An outpatient treatment clinic for gestational diabetes within a 250-bed tertiary care, non-profit hospital with a Parish Nurse partnership. Participants One hundred Mexican American women were included in the study with randomization into Parish Nurse Intervention Program (n=49) and care as usual (n=51) groups. Main Outcome Measures The Health Promoting Lifestyle Profile II (HPLP II) and two measures of glycemic control pre- and post-intervention, as well as newborn size, and days of maternal and neonatal hospitalization. Results Outcomes indicate significantly improved Health Promoting Lifestyle Profile II scores in the Parish Nurse Intervention Program group post-intervention compared with the Care As Usual group. No significant differences between groups regarding glycemic control, macrosomia, or days of maternal or neonatal hospitalization were found. Conclusions A Parish Nurse Intervention Program for pregnant women of Mexican descent with gestational diabetes is effective in leading to improved self-reported health promoting behaviors.