\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
  \draw (0,0) circle [radius=1.5];
  \draw (0,0) circle (2cm); % old syntax
  \draw (0,0) circle [x radius=1.5cm, y radius=10mm];
  \draw (0,0) circle (1.2cm and 8mm); % old syntax
  \draw (0,0) circle [x radius=1cm, y radius=5mm, rotate=30];
  \draw[rotate=30] (0,0) ellipse (20pt and 10pt);  % old syntax
\end{tikzpicture}
\end{document}