Menus longer than ten items become hard for users to scan and use.
In fact, the optimal length for a menu is probably closer to seven items. (The classic study of this issue is The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information.)
To avoid this problem, longer collections of pages need to be organized into groups. (See the navigation of this guide, which splits up more than forty pages into five different menus, as an example.)
The major exception to this practice is a menu that has a clear numeric or alphabetic organization.
A list of semesters—ordered by year—or of faculty—alphabetized by name—will not present major usability problems. However, if the content on the page is short, the menu may extend beyond the content area of the page, or even below the footer of the page, which presents its own usability problems.