The interface design of a Chiari malformation hypermedia document was tested with formative evaluation, a type of usability testing. The evaluation tested six common interactive design features essential for the design of user-friendly interfaces: image, size, label highlighting, text presentation (scrolling vs. hyperlinks), color (text, visual material, and background), and button behavior. Six neurosurgical residents answered a questionnaire focusing on these interactive design features during the development of the hypermedia document. Over a period of two months, the responses to the questions and suggestions made by the volunteers were used to improve the six interactive design features for the specific target audience of Toronto Hospital, Western Division neurosurgical residents.