Historical and psychophysical literature has demonstrated a perceptual interplay between olfactory and auditory stimuli—the neural mechanisms of which are not understood. Here, we report novel findings revealing that the early olfactory code is subjected to auditory cross-modal influences. In vivo extracellular recordings from the olfactory tubercle, a trilaminar structure within the basal forebrain, of anesthetized mice revealed that olfactory tubercle single units selectively respond to odors—with 65% of units showing significant odor-evoked activity. Remarkably, 19% of olfactory tubercle single units also showed robust responses to an auditory tone. Furthermore, 29% of single units tested displayed supraadditive or suppressive responses to the simultaneous presentation of odor and tone, suggesting cross-modal modulation. In contrast, olfactory bulb units did not show significant responses to tone presentation nor modulation of odor-evoked activity by tone—suggesting a lack of olfactory–auditory convergence upstream from the olfactory tubercle. Thus, the tubercle presents itself as a source for direct multimodal convergence within an early stage of odor processing and may serve as a seat for psychophysical interactions between smells and sounds.