The butterfly fauna of the Boabeng-Fiema Monkey Sanctuary in Ghana is reviewed in detail. The Sanctuary covers just 1.9 km² but only parts are truly forested. It is situated in the extreme north of the original forest zone and is currently isolated from any larger forests by some 50 km of derived savanna and farmbush. It has survived only because it provides the essential habitat for two species of monkey that are revered by the local communities. Surveys indicate that the present butterfly fauna is about 375 species, which is impressive for a tiny forest in far from pristine condition. Comparison with other forests in Ghana indicates that it would have contained about 500 species when it was part of a larger, contiguous forest system. It would thus seem that the small size and increasing isolation has so far led to a loss of no more than 125 species (25 % of its original fauna), which includes most of the endemic and rarer species in the country. A larger number of butterflies appears to survive in small forest fragments than is the case with birds. Continued monitoring would be interesting in its own right, but also because forest fragments are potentially important as stepping stones between the increasingly isolated major forests of Ghana.