Signout is an unofficial clinical document used traditionally to facilitate patient handoff. Qualitative studies have suggested its importance in clinical care. We used a novel technique to quantify the use of signout by analyzing clinical information system logfiles. Viewing and editing events were collected for 1,677 unique patients admitted to our internal medicine service. We found the average patient's signout on a given day is viewed frequently (>6x) and edited frequently (>2x) with multiple unique viewers (>3) and editors (>1). We also found that signouts are used throughout a 24-hour period, not just at the time of handoff. Finally, we showed that they are viewed months and even years after their creation. Signout is therefore a highly utilized, collaborative, clinical document used for more than patient handoff. Our findings also suggest that clinical information systems may benefit from the introduction of collaborative tools such as subscription, versioning, and author-attribution utilities.