[throwaway_374]

Thanks for your reply but I have no idea why this is the top voted reply as it does not consider my factors . As noted by others:

1) The doctor/practice does not have my latest mobile phone number as I have not been to them in years. Having said that, it may be an old number on which I used to use Facebook. This friend suggestion is only in the past few months, which suggests that they are mining friend circles in historic usage data - everyone you know, and ever knew. All that being said, this would require my doctor to have my personal mobile number on her personal mobile phone on which she would have used Facebook at some point in time, which is absolutely impossible in a professional setting.

2) I have not installed Facebook on my current phone.

I'm still not convinced by any argument here, beyond the doctor actively looking me up on Facebook personally outside work.

[compsciphd]

1) the doctor might have only uploaded their contacts to facebook recently

2) my argument has nothing to do with your phone, just what info you have given facebook (email/phone number). If someone else uploads their contacts that includes one of those pieces of information, facebook makes a connection.