Inspired by the acquisition–cognition–application model (T. Saracevic & K.B. Kantor, 1997), we developed a tool called the Information Assessment Method to more clearly understand how physicians use clinical information. In primary healthcare, we conducted a naturalistic and longitudinal study of searches for clinical information. Forty-one family physicians received a handheld computer with the Information Assessment Method linked to one commercial electronic knowledge resource. Over an average of 320 days, 83% of 2,131 searches for clinical information were rated using the Information Assessment Method. Searches to address a clinical question, as well as the retrieval of relevant clinical information, were positively associated with the use of that information for a specific patient. Searches done out of curiosity were negatively associated with the use of clinical information. We found significant associations between specific types of cognitive impact and information use for a specific patient. For example, when the physician reported “My practice was changed and improved” as a result of this clinical information, the odds that information was used for a specific patient increased threefold. Our findings provide empirical data to support the applicability of the acquisition-cognition-application model, as operationalized through the Information Assessment Method, in primary healthcare. Capturing the use of research-based information in medicine opens the door to further study of the relationships between clinical information and health outcomes.