Person-centered planning is central to United Kingdom policies regarding the support of people with intellectual disabilities. However, little evidence exists on the impact or cost of introducing person-centered planning. We examined the efficacy, effectiveness, and costs of introducing person-centered planning for 93 people with intellectual disabilities over 2 years across four localities in England. A person-centered plan was successfully developed for 65 people. Little change was apparent prior to introducing person-centered planning. After its introduction, modest positive changes were found in the areas of social networks; contact with family; contact with friends; community-based activities; scheduled day activities; and choice. The direct training and support cost of introducing person-centered planning was $1,202 per participant; indirect costs were negligible.