Background: Clinical practice guidelines (CPGs) have become a very popular tool for decision making in healthcare. While there is some evidence that CPGs improve outcomes, there are numerous factors that influence their acceptability and use by healthcare providers. While evidence of clinicians' knowledge, perceptions and attitudes toward CPGs is extensive, results are still disperse and not conclusive. Our study will evaluate these issues in a large and representative sample of clinicians in Spain. Methods/Design. A mixed-method design combining qualitative and quantitative research techniques will evaluate general practitioners (GPs) and hospital-based specialists in Spain with the objective of exploring attitudes and perceptions about CPGs and evidence grading systems. The project will consist of two phases: during the first phase, group discussions will be carried out to gain insight into perceptions and attitudes of the participants, and during the second phase, this information will be completed by means of a survey, reaching a greater number of clinicians. We will explore these issues in GPs and hospital-based practitioners, with or without previous experience in guideline development. Discussion. Our study will identify and gain insight into the perceived problems and barriers of Spanish practitioners in relation to guideline knowledge and use. The study will also explore beliefs and attitudes of clinicians towards CPGs and evidence grading systems used to rate the quality of the evidence and the strength of recommendations. Our results will provide guidance to healthcare researchers and healthcare decision makers to improve the use of guidelines in Spain and elsewhere. © 2010 Kotzeva et al; licensee BioMed Central Ltd.