The objective of this study was to determine the relationship between prescribed daily dose frequency and patient medication compliance. The medication compliance of 105 patients receiving antihypertensive medications was monitored by analyzing data obtained from special pill containers that electronically record the date and time of medication removal. Inaccurate compliance estimates derived using the simple pill count method were thereby avoided. Compliance was defined as the percent of days during which the prescribed number of doses were removed. Compliance improved from 59.0% on a three-time daily regimen to 83.6% on a once-daily regimen. Thus, compliance improves dramatically as prescribed dose frequency decreases. Probably the single most important action that health care providers can take to improve compliance is to select medications that permit the lowest daily prescribed dose frequency.