For most visitors to Rwanda, the best time to visit is during the dry seasons (from December to early February and June to September) when the conditions are ideal for gorilla trekking. The trails are much easier to negotiate and there’s far less risk of contracting malaria. That being said, you can trek to see the gorillas outside of these seasons, provided you’re willing to deal with muddy trails. For many visitors, being able to secure one of the in-demand gorilla trekking permits determines when they visit.  If you’re visiting Rwanda to see the chimpanzees in Ngungwe, then the rainy seasons from mid-February to early June and mid-September to mid-December are best. Food is easier to find during these periods so the primates don’t venture as deep into the forest (making them more difficult to spot).