Will a fistula in ano without surgery lead to serious problems if I don't have surgery?

Anal Fistula. Anal fistula should usually be addressed. Normally this is done with surgery. In patients with crohns disease, sometimes asymptomatic fistulae do not require treatment. Otherwise not treating a fistula can leave one at risk for infection, abscess, life threatening infection, and over a period of years, possibly cancer developing in the fistula tract.
Not necessarily. There are different levels of fistula and they should be treated properly. Untreated, they may cause continuous problems with abscesses and infections.