Participants in controlled feeding studies must consume all study foods and abstain from all other foods. In outpatient studies in which adherence may be compromised by free-living conditions, promoting, documenting, and monitoring dietary adherence are necessary. In the Dietary Approaches to Stop Hypertension (DASH) trial, a thorough participant screening process, an orientation session, and a run-in feeding period before randomization aided in the selection of participants who would most likely adhere to the demands of the study protocol. Throughout the feeding period, various educational and motivational techniques were used to encourage DASH participants to adhere to the dietary protocol. Both objective and subjective methods documented excellent participant adherence. Daily monitoring of individual adherence was based on meal attendance, body weight measurements, and daily diaries. Urinary sodium, potassium, phosphorus, and urea nitrogen values and an anonymous poststudy survey were used to evaluate adherence at the end of the study. Most DASH participants adhered to the feeding regimen by consuming only study foods and no other foods. When adherence lapsed, participants generally cited the lack of menu variety as a reason. Successful participant adherence to the constraints of an outpatient controlled feeding study is possible with carefully selected participants and a variety of adherence-promoting strategies incorporated into the study protocol.