Traditional rehabilitation research involves designs emphasizing between-subject statistical evaluation and comparisons across two or more groups. The argument is made that these designs are often of limited use in clinical environments characterized by small samples and large within-group variability. The idiographic model of research design is presented as on alternative to traditional group comparison design. Idiographic, or single-subject, research emphasizes continuous monitoring of patient performance within a specified design framework. The advantages and limitations of both single-subject and group comparison designs are presented. Both designs can help establish the efficacy of rehabilitation practice and contribute to rehabilitation science.