Ten adolescent clients of a Midwestern residential /school treatment facility for people with severe developmental disabilities participated in this case-control study. The control group participated in the standard Student Support Plan including 30 min of leisure activity 3 times per week. The treadmill walking group (TWG) were given additional opportunities to engage in treadmill walking during these sessions as well as on days in which no activity was allotted and during evening hours in their residence. Efficacy was defined as a significant progression in treadmill walking frequency, speed, elevation, and monthly calories expended coupled with a reduction in BMI.