Context: Only a minority of women with diabetes attend prepregnancy care service and the economic effects of providing this service are unclear.Objective: The objective of the study was to design, put into practice, and evaluate a regional prepregnancy care program for women with types 1 and 2 diabetes.Design: This was a prospective cohort and cost-analysis study.Setting: The study was conducted at antenatal centers along the Irish Atlantic Seaboard.Participants: Four hundred fourteen women with type 1 or 2 diabetes participated in the study.Intervention: The intervention for the study was a newly developed prepregnancy care program.Main Outcome Measures: The program was assessed for its effect on the risk of adverse pregnancy outcomes. The difference between program delivery cost and the excess cost of treating adverse outcomes in nonattendees was evaluated.Results: In total, 149 (36%) attended: this increased from 19% to 50% after increased recruitment measures in 2010. Attendees were more likely to take preconception folic acid (97.3% vs 57.7%, P < .001) and less likely to smoke (8.7% vs 16.6%, P = .03) or take potentially teratogenic medications at conception (0.7 vs 6.0, P = .008). Attendees had lower glycated hemoglobin levels throughout pregnancy (first trimester glycated hemoglobin 6.8% vs 7.7%, P < .001; third trimester glycated hemoglobin6.1% vs 6.5%, P = .001), and their off spring had lower rates of serious adverse outcomes (2.4% vs 10.5%, P = .007). The adjusted difference in complication costs between those who received prepregnancy care vs usual antenatal care only is (sic)2578.00. The average cost of prepregnancy care delivery is (sic)449.00 per pregnancy.Conclusions: This regional prepregnancy care program is clinically effective. The cost of program delivery is less than the excess cost of managing adverse pregnancy outcomes.