Hofmann elimination of N,N,N-trimethylcyclooctylammonium hydroxide has been found to give a mixture of cis- and trans-cyclooctene. The trans-cyclooctene is formed by a 100 % syn mechanism with a syn kH/kD = 1.94. The cis-cyclooctene is formed by a 51% syn mechanism and 49% anti mechanism. An anti kH/kD = 2.64 for the anti elimination to form cis-cyclooctene is calculated. The importance of these results is discussed. © 1968, American Chemical Society. All rights reserved.