Bali is one of Southeast Asia's safest destinations for tourists. Violent crime is rare. The main concerns are petty theft (don't leave valuables visible on the beach or in a car), traffic accidents (scooter rental is convenient but Bali's roads claim many tourist lives — wear a helmet and assess your riding skill honestly), and scams at tourist sites.
Natural hazards: Mount Agung and Mount Batur are active volcanoes — check current activity levels and evacuation zones before visiting. Rip currents at surf beaches (Kuta, Uluwatu) are dangerous for non-swimmers — swim only at supervised beaches. Bali belly (traveler's diarrhea) affects many visitors — be careful with street food hygiene, ice, and salads.