Abstract There is considerable literature on nurse-managed clinics and client satisfaction with nurse practitioner care. However, the methodological weaknesses of satisfaction measures which are often used limits confidence in the study findings. Satisfaction measures typically lack reliability analysis and/or have limited validity testing. This descriptive, correlational study investigates the validity and reliability of a new measure, the Client Satisfaction Tool (CST) and determines the degree of satisfaction that clients at a newly established senior health clinic had with the primary care services they were receiving. The CST is based upon Cox's Interactional Model of Client Health Behavior and thus was explicitly developed to measure client satisfaction with a nurse practitioner model of care. A convenience sample of 38 clients completed the CST. Responses to the CST indicated that users of the senior health clinic were satisfied with the care they received. Reliability testing showed that the tool has high internal consistency (Chronbach's alpha was 0.956) and high stability (r= 0.974). Construct validity testing with measures of perceived health changes showed that the tool has both convergent (r= 0.599, P≤ 0.01) and divergent (r= 0.194, P > 0.10) validity. Thus, the CST is a methodologically sound measure of client satisfaction that can be used in future research that examines client satisfaction with nurse practitioner care.