Open access scheduling attempts to provide access to care at the point it is needed. Under open access, when a parent calls to schedule a well-child visit, the patient would be seen within 1 or 2 days in contrast to usual systems of 4- to 6-week delays. In this randomized controlled trial involving 10 providers and 878 infants, providers were randomized to either open access for future visits or open access for current visits. In both groups, missed appointment rates dropped dramatically, although more so among the same-day open access group. Immunization rates increased in both groups; provider continuity was higher in the group with open access for future visits.