OBJECTIVE: To describe the obstacles encountered when attempting to answer doctors' questions with evidence. DESIGN: Qualitative study. SETTING: General practices in Iowa. PARTICIPANTS: 9 academic generalist doctors, 14 family doctors, and 2 medical librarians. MAIN OUTCOME MEASURE: A taxonomy of obstacles encountered while searching for evidence based answers to doctors' questions. RESULTS: 59 obstacles were encountered and organised according to the five steps in asking and answering questions: recognise a gap in knowledge, formulate a question, search for relevant information, formulate an answer, and use the answer to direct patient care. Six obstacles were considered particularly salient by the investigators and practising doctors: the excessive time required to find information; difficulty modifying the original question, which was often vague and open to interpretation; difficulty selecting an optimal strategy to search for information; failure of a seemingly appropriate resource to cover the topic; uncertainty about how to know when all the relevant evidence has been found so that the search can stop; and inadequate synthesis of multiple bits of evidence into a clinically useful statement. CONCLUSIONS: Many obstacles are encountered when asking and answering questions about how to care for patients. Addressing these obstacles could lead to better patient care by improving clinically oriented information resources.