Sue, generally speaking yes it is safe. Obviously pick a reputable tour company, independent travel is a much riskier prospect. Kigali has has and continues to have occasional trouble - there were some grenade attacks in early 2011, and although not a basket case anymore there is some political volatility. Stay well away from demonstrations and protests if there are any.
Several foreign governments advise their citizens to stay away from the borders with Burundi and Democratic Republic of Congo (with the exception of Gisenyi, Kibuye and Cyangugu). Where you're heading is close to the DCR border - which is why it's doubly important to pick a reputable tour company to take you up to the gorillas. about 6 years ago