Rum and cachaça are sugarcane distillates produced on large scales and of similar composition, and their differentiation is currently a subject of commercial dispute and a challenging analytical task. We have investigated the ability of direct-infusion electrospray ionization mass spectrometry in the negative ion mode, i.e. ESI(-)-MS, to distinguish between samples of these distillates. ESI(-)-MS fingerprints were collected for some samples of Brazilian artisan cachaça, aged in two types of wooden casks, i. e. amburana (Amburana cearensis) and jequitibá (Cariniana estrellensis), and of commercial rum. The mass spectra were found to be very distinctive, showing sets of diagnostic ions for each type of sample, i. e. (1) cachaça aged in amburana (m/z 271, 313, 377) and jequitibá (m/z 171, 255, 455) casks; and (2) commercial rum (m/z 89, 97, 179, 255, 283). When applied to the ESI(-)-MS data, principal component analysis and hierarchical cluster analysis split rum and cachaça samples into well-defined groups. Moreover, the two types of cachaça samples aged in wooden casks of amburana or jequitibá were also split into two distinct groups. Direct-infusion ESI(-)-MS can therefore be potentially applied to the rapid, simple, and accurate differentiation of these commercially important sugarcane distillates.