Even though Turkey is relatively safe, the only crime-free place is heaven, so here are things to watch:

STREET CRIME: it has begun to grow in the big cities (Ankara, Istanbul, Izmir), particularly in tourist areas: pickpockets and bag-snatchers. Defense is the same anywhere: wear your purse/bag strap over your chest (not just dangling from your shoulder) and hold your bag close. Details...

Mugging (robbery) and rape are rare, but they do happen, so observe the normal travel precautions. Details...

Single male travelers should beware two particular scams aimed at them: "Let's Have a Drink" and "New Traveling Companions," one of which even happens on trains.

Women travelers should be sensitive to local customs and attitudes.

TERRORISM: it's everyone's worry these days. Statistically, it is not much of a danger at all (compared to such real big-time killers as traffic accidents), but it makes headlines, so we're frightened. More...

You must answer this question to fit your personal tolerance for risk. If you believe the statistics and look at it rationally, you'll probably go. If you're going to worry about safety a lot while you're there, the worry may make your trip less pleasant, and so you probably shouldn't go.