It somewhat depends on how much mapping the players are doing.
If they are going old school, and drawing what you describe "you are in a 50' long corridor with a door at the end and doors on either side 20' from the end" your challenge is much greater than if you are being less specific in your descriptions, and they are not drawing a map. "You are in a long corridor with a door at the far end, and doors on either side, just past the midpoint".
In the later case, any time the players want to go to a specific location (rather than forwards to the next room), have them make dungeoneering tests. The farther they are trying to go the harder the DC and the more random a location they wind up in on a failure.
In the former case, perhaps you could note down their dungeoneering bonus, and before giving them details, roll dungeoneering - if they fail, get something wrong, or omit something from the description. If something comes up, like a combat or they go back the way the came, or come to an "impossible" situation like a room where they had already mapped, and should encounter the mistake, You can always say something like "Oh yeah... there were two doors on that wall, not just the one.", or "You didn't notice before, but the hallway does slope a great deal".
[continued - based on the comment that the players are very exacting mappers]
When asking for dungeoneering tests when players are asking for exacting measurements, and feel free to give bonuses for creative use of time and equipment, and penalties for lighting conditions and pressurized situations (fleeing from monsters, caught in on a raft in a raging current) not conducive to good mapping.
Do this even when you don't expect them to get lost, to train them to expect that they may get things wrong in their map.
Dungeon elements that do not lend themselves to good simple mapping techniques can be used to introduce further error, such as curved (measuring the actual curvature of the passage is not easy), twisty, sloped or down, really long stairs, and especially combinations of the elements are going to be very difficult for the characters to get exacting readings on.
I would describe these elements like "you think that the stairs traveled a net 80' north, 15' east and 60' down, but their twisty, uneven nature makes you slightly unsure"
By getting the players to miss-map a few elements, you can introduce worry by having them enter a room that (according to their map) exists in the exact same place as another area they have already mapped.
Having the characters chased by monsters (or vice versa, having the characters chasing a monster) through a room with many branches can add a significant source of error into their maps.... if they run through a room with 10 exits on the side they entered via, can they really be sure which one they entered from?