99DOTS is an unobtrusive, inexpensive adherence monitoring approach first piloted on a large scale in India. Patient medications (pill blisters) are packaged in a custom, secondary envelope with a series of unpredictable, hidden phone numbers that are revealed each time a patient takes his/her medication. Patients are asked to call the revealed numbers to let healthcare workers know that they have taken their medication. The use of these unpredictable, hidden numbers is intended to increase the accuracy of selfreported information by confirming that the medication is ‘in hand.’