  We establish a prime number theorem for all uniquely ergodic, analytic skew
products on the $2$-torus $\mathbb{T}^2$. More precisely, for every irrational
$\alpha$ and every $1$-periodic real analytic $g:\mathbb{R}\to\mathbb{R}$ of
zero mean, let $T_{\alpha,g} : \mathbb{T}^2 \rightarrow \mathbb{T}^2$ be
defined by $(x,y) \mapsto (x+\alpha,y+g(x))$. We prove that if $T_{\alpha, g}$
is uniquely ergodic then, for every $(x,y) \in \mathbb{T}^2$, the sequence
$\{T_{\alpha, g}^p(x,y)\}$ is equidistributed on $\mathbb{T}^2$ as $p$
traverses prime numbers. This is the first example of a class of natural,
non-algebraic and smooth dynamical systems for which a prime number theorem
holds. We also show that such a prime number theorem does not necessarily hold
if $g$ is only continuous on $\mathbb{T}^2$.
