Because of differences in education and role preparation, nurse practitioners (NPs) and physicians (MDs) may assume either complementary or substitutive roles in patient care. To describe role complementarity and similarity, the role perceptions of 15 NPs and 15MDs in joint practice were assessed. Ten NP and MD respondent pairs were selected from a variety of ambulatory primary care settings (urban, rural, public, private, and health maintenance organizations), and five NP-MD pairs were chosen at random. A questionnaire of nine patient vignettes was created; respondents rated the appropriateness of their role in managing the clients described in each vignette using an 8-point scale. Significant differences existed between NP and MD perceived roles for six vignettes, p less than .05. NPs identified as highly role appropriate those vignettes necessitating psychosocial support and health education; MDs identified as highly role appropriate vignettes representing high risk physical conditions. The differences in NP and MD role perception were complementary.