  We present an analysis of the decay $D^0 \to K^+\pi^-$ based on FOCUS data.
  From a sample of 234 signal events, we find a branching ratio of
$\frac{\Gamma(D^0 \to K^+\pi^-)}{\Gamma(D^0 \to K^-\pi^+)} =
(0.429^{+0.063}_{-0.061}\pm 0.027)%$ under the assumptions of no mixing and no
CP violation. Allowing for CP violation, we find a branching ratio of $(0.429
\pm 0.063 \pm 0.028)%$ and a \textit{CP} asymmetry of $0.18 \pm 0.14 \pm 0.04$.
The branching ratio for the case of mixing with no CP violation is
$(0.381^{+0.167}_{-0.163} \pm 0.092)%$. We also present limits on charm mixing.
