83-year-old Joan Bonner was last seen at a bus stop on Congham Road at West Pymble, about 3pm on Thursday.
There are concerns for her welfare as she requires medication that she may not have with her.
Ms Bonner is described as being of Caucasian appearance, about 152cm tall, with a slim build and short grey hair
She was last seen wearing a grey suit and a dark coloured beret style hat, and was also carrying a white walking stick with a distinctive floral pattern.
Ms Bonner may appear confused and disorientated and does not have access to a mobile phone.