Cycads and colobus monkeys occur together in many parts of tropical Africa; we present the first records of colobus feeding on these plants. On 22 occasions, the Endangered Zanzibar red colobus Procolobus kirkii fed on the leaves of Encephalartos hildebrandtii, a Near Threatened species, in the Kiwengwa-Pongwe Forest Reserve, north-eastern Unguja. A total of 92 minutes of cycad feeding were observed during a 14-month, 678-hour study of three focal groups, suggesting rare but consistent use of cycads. We analyzed HCN content in a small sample of browsed and unbrowsed cycad leaves for a preliminary analysis of toxicity, but toxicity was similar (and high) across leaves. Colobus appear to be one of the few mammal species able to exploit this abundant food source (277 cycads/ha) in the 33 km² coral rag forest. Both colobus and cycads of this region need urgent protection; in August 2011, much tree cutting was observed resulting in a discontinuous canopy which will threaten both colobus and cycads.