Efforts at predicting long-term adherence to medications have been focused on patients filling typical month-long supplies of medication. However, prediction remains difficult for patients filling longer initial supplies, a practice that is becoming increasingly common as a method to enhance medication adherence. The objective of this retrospective cohort study was to extend methods involving short-term filling behaviors and develop novel variables to predict adherence using claims from a larger national insurer in a cohort of patients receiving longer initial prescriptions for diabetes, hypertension and hyperlipidemia (specifically statins).