The mod-$p$ cohomology rings of some $p$-groups Ian J. Leary Faculty of Mathematical Studies, University of Southampton, Southampton SO17 1BJ, United Kingdom. Abstract We determine the mod-$p$ cohomology rings of an infinite family of $p$-groups, for odd primes $p$, with cyclic derived subgroups. Our method involves embedding the groups in a compact Lie group of dimension one, and was suggested by P. H. Kropholler and J. Huebschmann. Math. Proc. Camb. Phil. Soc. 112 (1992), 63-75.