As part of the monitoring of lion populations in the Pendjari Biosphere Reserve, which began in 2001, the fourth census of lions in the said reserve took place from 20 April to 22 May 2009. The results indicate a density of 0.015 lions/km² and 0.015 hyens/km². Since the density of lions was 0.0067 lions/km² in 2002 and 0.005 lions/km² in 2004, these results indicate an improvement in the status of lion populations in Pendjari. This increase in density is also reflected in the higher contact rate and group composition than in previous years. This testifies to the success of CENAGREF's conservation actions on lion populations in Pendjari. However, the observation of inadequacies in data collection by tourists and others in previous years remains current. Moreover, as calling operations are beginning to become too frequent to guarantee the reliability of call results, it would be appropriate to observe a rest period of a few years before starting again with the count. Hence the need for regular monitoring by hunting guides, eco-guards and tourist guides.