RATIONALE AND OBJECTIVES. Information overload is a significant problem for the modern radiologist. This prospective study compares the instructional effectiveness of a multimedia textbook (HyperLung) with a lecture. HyperLung is a radiologic multimedia textbook about imaging diffuse lung disease created using a multimedia authoring tool, the Annotator (the University of Iowa Second Look Computing, Iowa City, IA), on the Apple Macintosh computer (Apple Computer, Cupertino, CA). METHODs. Forty-nine staff physicians and residents in the Department of Radiology were randomized to receive instruction either by HyperLung or by a lecture. The instructional content was the same in both groups, and both groups were tested before and after instruction. The actual time spent in each instructional situation was recorded. RESULTS. The instructional effectiveness of the multimedia textbook and lecture was equal. The instructional efficiency of HyperLung was only 60% of the lecture. Users of the multimedia textbook found it enjoyable and straightforward to use. CONCLUSIONS. Multimedia textbooks have a promising future in radiology education.