The medical care system is not very effective in modifying health behavior of individuals, in particular, ensuring patient compliance with medication regimens, healthy diets, regular physical activity, and regular health screening, and in the avoidance of substance abuse. Telephone-Linked Care (TLC) is a telecommunications technology that enables computer-controlled telephone counseling with patients in their homes. It has been applied to the task of improving a number of different health behaviors. Randomized controlled studies suggest that use of the system for as little as 3 months is associated with improvement in adherence to medication regimens, dietary change in hypercholesterolemia, and increased physical activity among sedentary individuals. Future work involves applying the technology to other important health behaviors, optimally using health behavior theory in the system design, targeting use of TLC to the most appropriate patient groups, incorporating new computer and telecommunications technology into the system, and interfacing TLC into the health care delivery system.