The healthcare industry is increasingly turning to billboard advertising to promote various medical services, yet little attention has been directed toward understanding the performance and policy implications of billboard advertising from the perspective of the patients targeted. To shed light on this, we initiated a field experiment investigating the impact of an urgent care center's billboard advertising campaign, collecting primary data over a 32-day period at the center's two clinics. Over the course of the billboard campaign, perspectives from 1,640 patients were collected via questionnaire. Institutionally supplied business metrics were also monitored. Our principal findings indicate that billboard advertisements are noticed by patients, favorably viewed by patients, and effective across the sequence of steps leading to patient patronage. Enhancement of awareness exerts the most powerful influence on patronage, but the capacity to inform consumers is also highly significant. These effects are not limited to new patients, as many returning clients were made more aware of the clinics and were influenced by the campaign. The study offers insights for creative billboard treatments and campaign planning. Although effects remained strong throughout the campaign, some degree of "wearout" was evident after three weeks, which suggests the need to rotate billboards frequently and to consider digital billboards. Corner tabs--small announcements sometimes placed in the corners of billboard advertisements--proved largely ineffective as a promotional device and may clutter the central messages. Given these findings, we believe healthcare institutions are justified in using billboards, as they perform effectively and appear relatively free of controversy. Careful planning of creative billboard treatments and appropriate scheduling patterns are essential to maximize their communications potential.