A woman was bitten by a dog in Baulkham Hills on Saturday afternoon while walking with her toddler.
About 4pm, the 59-year-old woman was walking on Oakland Avenue with an 18-month-old boy while carrying a small dog.
The woman was bitten on the arm by a dog she believed to be a German shepherd. It then ran away.
She was taken to hospital for treatment. The child was not injured.
Police are yet to determine the dog involved in the incident, and would like to hear from anyone who may be able to help with the investigation.
Anyone with information should call Crime Stoppers on 1800 333 000 or online at http://police.nsw.gov.au by clicking on the "Help us solve a crime" tab.