In this paper, we study the existence, nonexistence, and multiplicity of positive solutions to a nonlinear impulsive Sturm–Liouville boundary value problem with a parameter. By using a variational method, we prove that the problem has at least two positive solutions for the parameter $\lambda \in (0,\Lambda )$
λ
∈
(
0
,
Λ
)
, one positive solution for $\lambda =\Lambda $
λ
=
Λ
, and no positive solution for $\lambda >\Lambda $
λ
>
Λ
, where $\Lambda >0$
Λ
>
0
is a constant.