We attempted to clarify the anatomic relationships of the lacrimal sac by performing standard orbital dissections to expose the lacrimal canaliculi, lacrimal sac, the ethmoid air cells, nasal septum, frontal sinuses, and the cribriform plate in five human cadaver heads; and then measuring the distance between the internal common punctum (ICP) and five key structures. The mean vector distance from the ICP to the anterior aspect of the cribriform plate was 25.1 +/- 2.95 mm. This measurement, along with the others, helps clarify osteotomy placement for dacryocystorhinostomy, so that, for example, cerebrospinal fluid leak can be prevented. Improved understanding of the anatomy of this region is also valuable in planning surgery for orbital and naso-orbital tumors, trauma, and congenital abnormalities.