A 5-month field study on both the distribution and ecology of Callimico goeldii was carried out in the seasonally dry rain forest of north-western Bolivia. The species was found to be very sparsely distributed (approximately one group per 4 kmsup2/sup) in isolated groups of about 6 animals throughout the study area. Callimico was found to associate a great deal with two species of Saguinus that inhabit the same region in greater densities. It appears to be a habitat specialist, preferring low-lying and damp, but well-drained, bamboo forest and spending nearly all its time within 3 m of ground level, travelling mainly by vertical clinging and leaping. We believe that this ecological specialisation accounts for the species’ discontinuous microdistribution, and that this in turn is related to Callimico’s distinctive pattern of social organisation.