OBJECTIVE: To determine whether low-income infants' adherence to nutritional supplementation with ferrous fumarate sprinkles was better than that with ferrous sulfate drops. STUDY DESIGN: The study was a randomized clinical trial of healthy 6-month-old infants. Each infant received either a daily packet of sprinkles or a dropperful of liquid. Follow-up included alternating telephone and home visits biweekly for 3 months. Adherence was defined as high if the infant's caregiver reported supplement use on 5 to 7 days during the week before assessment. Side effects and caregiver attitude about supplements were secondary outcomes. Analyses were conducted using generalized estimating equations and chi(2) and Wilcoxon rank-sum tests. RESULTS: A total of 150 of 225 eligible infants were enrolled. Adherence to supplementation was generally poor. High adherence ranged from 32% to 63% at any assessment in the subjects receiving drops, compared with 30% to 46% in those receiving sprinkles. The drops group was more likely to have at least four assessments with high adherence (22% vs 9.5%; P = .03). Caregivers of the drops infants were more likely to report greater than usual fussiness (P < .01); however, fussiness had no consistent impact on adherence. CONCLUSIONS: The use of ferrous fumarate sprinkles rather than traditional ferrous sulfate drops did not improve adherence with daily iron supplementation in low-income infants.