Background: Recent clinical trials indicate that treatment with lipid modifying therapy improves outcomes in patients with ischemic heart disease (IHD) and low levels of high density lipoprotein (HDL) cholesterol. The results of these trials, however, have not been widely implemented in clinical practice. Objectives: To develop and test an intervention designed to increase the rate of prescription of lipid modifying therapy and to determine the relative effectiveness of three different prompts (progress notes, patient letters, or computer chart reminders). Methods: The study was conducted in 11 US Department of Veterans Affairs Medical Centers. The effect of the intervention on the proportion of eligible patients receiving lipid modifying therapy was compared between five intervention sites and six matched control sites using a controlled before and after study design. Additionally, 92 providers within the intervention clinics were randomized to receive one of the three prompts. Data were analyzed using logistic regression modeling which incorporated terms to account for the clustered nature of the data. Results: At the intervention sites the prescription rate increased from 8.3% during the pre-intervention period to 39.1% during the intervention (OR = 6.5, 95% CI 5.2 to 8.2, p<0.0001) but remained unchanged at the control sites. The interaction between group (control v intervention) and time period was highly significant (p<0.0001). The adjusted odds of receiving a prescription during the intervention period was 3.1 times higher at the intervention sites than at the control sites (95% CI 2.1 to 4.7). Overall, there was no significant difference in prescription rates among the three prompt groups. However, there was a significant interaction between prompt group and site, indicating that the efficacy of the prompts differed by site. Conclusion: An intervention for primary care providers consisting of an educational workshop, opinion leader influence, and prompts substantially increased the prescription rate of lipid modifying therapy.