What brings you here?

What brings you (around) here?

For what reason are you here? The word "you" is often emphasized, especially if the person's arrival or appearance is unexpected. What brings you around here, Tom? I feel like I haven't seen you in years. A: "Well, what brings you here today?" B: "I wanted to inquire about setting up a savings account for my son."
See also: bring, what
Farlex Dictionary of Idioms.

What brings you here?

Fig. What is your reason for being here? (A polite request for this information. More polite than "Why are you here?") Tom: Hello, Mary. What brings you here? Mary: I was invited, just like you. Doctor: Well, John, what brings you here? John: I've had this cough for nearly a month, and I think it needs looking into.
See also: bring, what
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • pearly
  • babysit with (someone or something)
  • it's what's inside that counts
  • it's what's on the inside that counts
  • (boy,) am I glad to see you!
  • Am I glad to see you!
  • sinking fast
  • cut of (one's) jib
  • vital statistics
  • conflict of interest