Background Periconception folate supplementation significantly reduces the risk of neural-tube defects, but few U.S. women start folate supplementation before pregnancy, and the amount of clinician time available to counsel patients about folate is limited. This study evaluated whether computer-assisted counseling and the provision of free folate tablets increases women's knowledge and use of folate supplements. Design Randomized controlled trial; follow-up began 6 months after enrollment and was completed on average 7 months after enrollment. Setting/participants A total of 446 women, aged 18–45 years, were recruited from two urgent care clinics in San Francisco from March to July 2005 (data collection was completed in 2006; data were analyzed in 2007). Intervention Participants received a 15-minute computerized educational session and 200 folate tablets. Main outcome measures The primary outcome was the knowledge that folate can prevent birth defects; secondary outcomes included the self-reported use of a folate supplement at follow-up. Results At follow-up, women in the intervention group were more likely to know that folate prevents birth defects (46% vs 27%, relative risk [RR]=1.72, 95% CI=1.32, 2.23); to know that folate is most important in early pregnancy (36% vs 17%, RR=2.11, 95% CI=1.50, 2.97); and to report the recent use of a folate supplement (32% vs 21%, RR=1.54, 95% CI=1.12, 2.13). Conclusions A one-time, brief, computerized counseling session about folate with the provision of free folate tablets increased the knowledge and use of folate supplements among women ≥6 months later. Trial registration NCT00177515.