Inspired by Sheehan’s conjecture that no
4
4
-regular graph contains exactly one hamiltonian cycle, we prove results on hamiltonian cycles in regular graphs and nearly regular graphs. We fully disprove a conjecture of Haythorpe on the minimum number of hamiltonian cycles in regular hamiltonian graphs, thereby extending a result of Zamfirescu, as well as correct and complement Haythorpe’s computational enumerative results from [Exp. Math. 27 (2018), no. 4, 426–430]. Thereafter, we use the Lovász Local Lemma to extend Thomassen’s independent dominating set method. This extension allows us to find a second hamiltonian cycle that inherits linearly many edges from the first hamiltonian cycle. Regarding the limitations of this method, we answer a question of Haxell, Seamone, and Verstraete, and settle the first open case of a problem of Thomassen by showing that for
k
∈
{
5
,
6
}
k \in \{5, 6\}
there exist infinitely many
k
k
-regular hamiltonian graphs having no independent dominating set with respect to a prescribed hamiltonian cycle. Motivated by an observation of Aldred and Thomassen, we prove that for every
κ
∈
{
2
,
3
}
\kappa \in \{ 2, 3 \}
and any positive integer
k
k
, there are infinitely many non-regular graphs of connectivity
κ
\kappa
containing exactly one hamiltonian cycle and in which every vertex has degree
3
3
or
2
k
2k
.