The delta H-2 and delta O-18 composition of 816 precipitation samples collected between February 2005 and October 2009 from four sites across the Sydney Basin, Australia, were analysed, representing the first published precipitation isotope dataset for the region. Monthly values, weighted averages and local meteoric water lines are presented for use in hydrological applications. The 4 year precipitation weighted average values ranged from delta H-2 = 20.16 parts per thousand, delta O-18 = 4.50 parts per thousand and d = 15.88 parts per thousand for Lucas Heights in the coastal region to delta H-2 = -29.48 parts per thousand, delta O-18 = -5.97 parts per thousand and d = 18.33 parts per thousand for Mt Werong in the highlands west of Sydney. For the Sydney Basin as a whole we recommend an overall local meteoric water line of delta H-2 = 8.01 +/- 0.05.delta O-18 + 16.8 +/- 0.3. Precipitation in the Sydney Basin is isotopically different from the nearest GNIP sites with a significantly higher D-excess. High D-excess values may be the result of low humidity at the sea surface during evaporation at mid latitude sources, however recycling of moisture either locally or along a moisture transport trajectory may also be an important factor. A clear coastal effect was observed but generally temperature and amount effects were found to be weak. © 2013, Elsevier Ltd.