We present the assessment of the land snail diversity in approximately 50 km² of savanna/forest mosaic in the northern part of Lopé National Park, Gabon, taking into account habitat variation and seasons. A total of 3,745 specimens were collected, yielding 74 species from 12 families, with Subulinidae being the most speciose family. Most specimens were not identified but assigned to Recognizable Taxonomic Units. Extrapolations suggest that the true diversity of the area lies between 79 and 132 species. Overall snail abundance was low, and most species were minute. Spatial and habitat heterogeneity was high, with 33.8% of the species collected from one station only. Rare species made up a considerable proportion of the fauna, with 23.0% of the species represented by one specimen only. The most species-rich habitats were mature forest, Marantaceae forest, rocky forest, and forest fragments isolated in savanna, in that order. Savanna was the least species-rich habitat, and no species were confined to this habitat. Benefits and drawbacks of the Recognizable Taxonomic Units approach are discussed, and suggestions for maximizing mollusc inventories in tropical forests are proposed.