A directory structure for WORM optical media which supports a multi-level tree structure containing several paths is disclosed. When a user defines the first path on the WORM volume, a first file directory group (140) is created for that path. A path directory entry pointing to this file directory group is written to the path directory group (130). Files having this path name are initially written into the first data file area (150) next to this file directory group. The first data file area grows as data is written into it. When a second path is defined, the first data file area is closed and a second file directory group (160) is created on the WORM volume next to the first data file area, thereby wasting little if any space. The path directory group is updated with a new path directory entry that points to this new file directo­ry group. Files having this second path name are written into a growing second data area. If the user now wants a file having the first path name to be written to the disk, a file directory entry is placed in the first file direc­tory group, but the file itself is written into the grow­ing second data file area. In this manner, files are associated with directory entries by a common path name, not necessarily physical location on the disk, although files tend to be relatively close to their associated directory entry.