Yes — Bissau is generally safe for tourists who take sensible precautions, though it requires more preparation than most African capital cities. Guinea-Bissau has experienced repeated coups and political instability since independence in 1974, and while daily life in Bissau is calm for the most part, the situation can change quickly. Check your government's travel advisory before and during your trip.
Petty crime (bag snatching, pickpocketing) exists, particularly around Bandim Market and at night. Avoid displaying expensive cameras, phones, or jewellery. Travel in groups after dark and use hotel-recommended taxis rather than unmarked vehicles.
Medical facilities are extremely limited — comprehensive travel health insurance including medical evacuation is essential. Malaria is endemic year-round; take antimalarials, use DEET insect repellent, and sleep under a mosquito net.
Generally, locals are welcoming and curious about foreign visitors. Engaging respectfully and learning a few words of Kriol goes a long way.