This study explores the role of similarity in the success of peer support relationships in an intervention program for dementia caregivers. Hypothesized predictors of successful matches included structural similarity between partners (e.g., in age, education), appraisal similarity (e.g., in satisfaction with support for caregiving), and psychological similarity (e.g., in psychological well-being). Contrary to expectations, no relationship between these types of similarity and the success of the match were found, but effects were found for dissimilar pairs on several characteristics. The findings suggest: 1) that what really makes a difference for successful peer support is sharing the stressful but also rewarding experience of caregiving; and 2) that program planners do not need to develop extensive matching criteria.