OBJECTIVES: To develop a pharmacist-provided educational intervention that instructs participants to consume 1,200 IU vitamin D daily and to evaluate its effect on serum 25-hydroxyvitamin D (vitamin D) concentrations and self-reported daily vitamin D intake in geriatric outpatients with insufficient vitamin D. DESIGN: Randomized controlled trial. SETTING: University-affiliated geriatric clinic, December 2005 to May 2006. PATIENTS: 80 participants aged 65 to 89 years. INTERVENTION: Participants with insufficient vitamin D (12-31 ng/mL) were randomized to receive either the educational intervention (n = 23) or no intervention (n = 22). MAIN OUTCOME MEASURES: Difference in change from baseline to 12 weeks in vitamin D concentrations and self-reported daily vitamin D intake between groups. RESULTS: At 12 weeks, vitamin D concentrations in the educational intervention group (n = 22) increased from a mean (+/- SD) of 23.5 +/- 5.0 to 30.4 +/- 6.3 ng/mL. Vitamin D concentrations in the nonintervention group (n = 21) increased from 22.8 +/- 5.4 to 26.9 +/- 6.2 ng/mL. The difference between the groups at 12 weeks did not reach statistical significance (P = 0.07). However, 12 participants (55%) in the educational intervention group achieved sufficient vitamin D concentrations compared with only 5 participants (24%) in the nonintervention group (P = 0.04). Self-reported daily vitamin D intake increased by a mean of 647 IU/day in the educational intervention group and 67 IU/day in the nonintervention group. The difference in self-reported intake between groups at 12 weeks, controlling for baseline, was significant (P < 0.0001). Serum parathyroid hormone concentrations decreased significantly among those in the intervention group (P = 0.04). CONCLUSION: A pharmacist-developed and -administered vitamin D educational intervention increased the proportion of participants achieving sufficient vitamin D concentrations, increased the self-reported daily vitamin D intake, and lowered serum parathyroid hormone concentrations. However, it did not significantly increase the overall mean serum vitamin D concentration, compared with the control group. A daily recommendation of more than 1,200 IU vitamin D daily is likely necessary to ensure that all geriatric outpatients with insufficient vitamin D concentrations achieve the target of at least 32 ng/mL.