\documentclass{article}
\usepackage{xypic}
\begin{document}

\def \objectstyle{\hbox}
\entrymodifiers={++[F-:<3pt>]}

\xymatrix@R=15pt{
VisitedAsia \ar[d]&*{}&*{}
& Smokes\ar[dl]\ar[dr]&*{}
\\
Tuberculosis\ar[dr]&*{} & LungCancer\ar[dl]
&*{} & Bronchitis\ar[ddll]
\\
 *{}& Or\ar[dl]\ar[dr] &*{} &*{} &*{}
\\
X-Ray &*{} & Dyspnea &*{}&*{}
}

\end{document}