Among animal seed dispersers in tropical ecosystems, the contribution of primates is recognized to be of paramount importance. However, the role played by the largest species of the Congo basin, the western lowland gorilla (Gorilla gorilla gorilla), has received little attention. Here, we provide the first long-term study describing all aspects of the ecology of seed dispersal by gorillas at a single site. Over three years of investigation in the forests of Mimpala, southeast Cameroon, we have identified 55 species whose seeds were found undamaged in 1030 faecal samples. On average, one faecal clump contained 2.4 seed species and 51.8 seeds. Gut passage, of a mean rate of 54.7h, does not affect viability of seeds and may even enhance germination success in some cases by separating the seed from the fruit pulp and/or by abrading the seed coat. As a result of habitat preference, seed deposition is biased towards open canopied environments, namely light gaps and young secondary forests. Monitoring of seedlings suggested that this directed-dispersal is an effective method of dispersal, as a significantly higher number of marked faeces still contained viable seedlings after one to two years in these habitats compared to the others. Quantitatively, this may be of benefit primarily to the tree genus Uapaca, as its seeds were found in almost half of all faecal clumps and its seedlings constituted the majority of the seedling cohort established in faeces. Furthermore, as a consequence of their heliophilous temperament, Uapaca seedlings were among those that developed the best at these seed deposition sites. We conclude that the western lowland gorilla may be a highly effective vector of secondary succession and its extirpation would likely have implications for forest dynamics.